How to Build a Shed Roof Step by Step: A UK DIY Guide

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Key takeaways

• Start square and level: a shed roof only works if the frame beneath it is true, so check everything with a spirit level before you fix a single board.
• Apex or pent? An apex roof has a central ridge and sheds rain well; a pent roof is a single slope that suits sheds placed against a wall.
• Use screws and exterior-grade materials: structural timber for the frame, exterior-grade OSB or tongue-and-groove boards for the deck, and quality felt applied from the bottom edge upward.
• Fit purlins carefully: these horizontal timbers support the roof deck, and gaps or unevenness here will cause sagging later.
• A well-built roof can last 10 to 15 years or more if you avoid the common mistakes listed below, according to shed specialists Shed UK.

What is the easiest type of shed roof to build in the UK?

The two most common shed roof designs in the UK are the apex roof and the pent roof, and both are well within reach of a competent beginner. An apex roof is the traditional pitched design with a central ridge running front to back, which gives good rain runoff and maximum headroom in the middle of the shed. A pent roof is a single sloping surface, which gives a more modern look and suits buildings positioned against a wall or fence.

For most first-time builders, a simple apex roof is the best place to start. The frame is symmetrical, the cutting is straightforward, and the pitched shape helps rain run off quickly, which matters in the British climate. According to DIY Sheds, the peak of an apex shed also gives plenty of headroom in the centre, making it the better choice if you want to stand up comfortably or store taller items.

What tools and materials do I need to build a shed roof?

Before you start, gather everything in one place. A checklist stops small omissions turning into mid-job trips to the builders’ merchant.

Materials

• Structural timber for the rafters, ridge board and joists, treated for outdoor use
• Exterior-grade OSB board or tongue-and-groove boards for the roof deck
• Roofing felt, sufficient to cover the roof with overlap at the edges
• Exterior-grade screws and felt nails or clout nails
• Galvanised fixings and, if desired, felt adhesive for the edges

Tools

• Saw (hand saw or circular saw) and a square for accurate cuts
• Spirit level and tape measure
• Cordless drill or driver
• Hammer, pencil, and a straight edge or chalk line
• Ladder and, ideally, a second pair of hands

Shed UK stresses that using quality materials ensures better weather resistance and a longer life, so resist the temptation to use whatever offcuts are in the garage for a roof that has to face UK weather year after year.

How do you frame an apex shed roof step by step?

Framing is the heart of shed roof construction. UK guides break the job into manageable stages, and the sequence below follows the approach described by Garden Buildings Direct and Shed UK.

Step 1: Check the shed walls first

Your roof sits on top of the walls, so the walls must be square, level and securely fixed. If you are starting from scratch, it is worth reading our companion guide on how to build a shed base step by step, because a level base is what makes a level roof possible.

Step 2: Cut and assemble the rafters

Cut your rafters to size, including any angled cuts needed at the ridge and where they meet the shed walls. Assemble the rafters on flat ground with a ridge board running along the top. Building the frame on the ground is far safer and easier than trying to assemble it in the air, and it lets you check that both sides match before lifting anything.

Step 3: Fix the frame to the shed walls

Lift the frame into place and fix it to the top of the shed walls, checking as you go that it is square and level. Garden Buildings Direct notes that the roof frame must be fixed securely and that everything downstream depends on this alignment. Use a spirit level as you work to confirm the frame is square and level before fixing it fully.

Step 4: Fit the purlins with no gaps

Purlins, sometimes called roof bearers, are the horizontal timbers that support the roof deck. On an apex roof, Garden Buildings Direct says they usually run front to back, across the width of the shed. Each purlin should be:

• Evenly spaced, with no large gaps that could cause sagging or weak spots
• Level across the top, checked with a spirit level, so the roofing sits flat
• Fixed to the frame using screws, not nails

If the purlins are off, the rest of the roof will not line up or hold steady, so treat this as the quality-control step of the whole build.

Step 5: Fix the roof boards

Fix your boards or panels in place, starting from the lowest edge or the back of the shed, and work across the frame one at a time. Keep each panel flush against the next: gaps will let in water or lead to movement over time. If you are using tongue-and-groove boards, slot each one fully into its neighbour before fixing it down.

Step 6: Let it dry, then felt it

Once the deck is complete, check it over for proud screw heads and splinters, sweep it clean, and you are ready for the covering stage.

How do you felt an apex shed roof correctly?

Felting is where a good frame becomes a weatherproof roof, and the golden rule is simple: work from the bottom edge upward. Shed UK recommends starting at the lowest edge so that each layer of felt overlaps the one beneath it, shingle-style, so water runs over the joints rather than into them.

Step by step

1. Cut the felt into strips long enough to run up the slope and over the ridge with overlap to spare.
2. Start at the eaves (the lowest edge). Lay the first strip and fix it along the bottom edge with clout nails or felt adhesive, leaving a small overhang at the eaves.
3. Lay the next strip so it overlaps the first by a good margin, and fix along its top edge only. Water flowing down the roof will pass over these fixings.
4. Continue to the ridge. At the apex, fold the felt over the ridge or add a separate ridge strip so no joins sit at the very top.
5. Trim the edges, fold the felt neatly around the sides, and fix securely along all edges.

Take care not to stretch the felt as you go, and avoid nailing it down so tightly that it tears in cold weather. A calm, dry day makes the job much easier, because wet or icy felt is slippery and stiff.

What are the most common shed roof mistakes to avoid?

Most failed shed roofs fail for boring reasons, and that is good news, because boring mistakes are easy to avoid. Based on the guidance from Shed UK and Garden Buildings Direct, watch out for these:

• Gaps between purlins or panels. Gaps cause sagging, weak spots and water ingress, so keep everything flush and evenly spaced.
• Nails instead of screws on the frame. Purlins and structural timbers should be screwed down; nails can work loose over time.
• An out-of-level frame. If the frame is not square and level when fixed to the walls, the boards and felt will not sit properly.
• Felting from the top down. Always start from the bottom edge and work upward so overlaps shed water.
• Using interior-grade materials. Only exterior-grade OSB or tongue-and-groove boards and outdoor-treated timber will cope with British weather.

Avoid these and, according to Shed UK, your roof can last 10 to 15 years or more.

Do you need plans to build a shed roof, or can you design it yourself?

You have two honest options. If you are comfortable with a tape measure and a bit of geometry, you can work out your own rafter lengths, angles and spacings. Many shed retailers, including DIY Sheds, offer free downloadable apex shed plans that can be customised to your exact measurements before you download the build instructions, which is a sensible starting point if you are building an apex shed from scratch rather than re-roofing an existing one.

If you would rather not design the roof yourself, a paid plan library such as My Shed Plans is worth a look. It is a large collection of ready-made shed and woodworking plans, sold as a digital download, which suits DIYers who want exact cutting lists and diagrams instead of working out angles from scratch. According to the seller, the plans cover a wide range of shed sizes and styles, including simple pitched designs like the one described above. It will not swing a hammer for you, and free plans (like the ones from DIY Sheds) remain a perfectly good option if your project is a single, standard build. Where My Shed Plans tends to suit people is when they expect to build more than one project, or want the reassurance of a fully worked-out design before they start cutting timber. As with any product, check exactly what is included before buying.

How long does building a shed roof take, and is it a beginner job?

How long the job takes will vary depending on the size of the shed, the complexity of the cuts and, inevitably, the British weather, so it is sensible to set aside plenty of time rather than rushing. The actual pace depends on the size of the shed, the complexity of the cuts and, inevitably, the British weather. Take the time to measure twice and cut once; rushing the rafter cuts is the most common cause of a roof that will not sit flush.

If you are happy with basic DIY tasks such as putting up shelving or following our guide on how to bleed a radiator, you have the practical skills needed here. The main requirements are accuracy, patience and a helper for lifting the frame into position. Working at height, even at shed-roof height, deserves respect: use a stable ladder, keep your work area tidy and never work on a wet roof surface.

Which roof covering should I choose for a UK shed?

Felt remains the standard covering for UK sheds because it is inexpensive, widely available and easy for beginners to apply. Shed UK notes that heavy-duty sheds may use thicker framing and stronger felt systems, so match the covering to the building: a small tool store needs far less than a workshop roof that will carry years of weather exposure.

• Standard mineral felt: the everyday choice for most apex sheds, applied from the bottom edge upward as described above.
• Heavy-duty or polyester-reinforced felt: thicker and more durable, suited to larger or heavily exposed roofs.
• Other coverings: options such as metal or bitumen sheets exist, but they require different fixings and are less forgiving for first-timers than felt.

Whatever you choose, the quality of the deck beneath matters as much as the covering on top. A smooth, flush, gap-free deck is what makes any felt job look tidy and last well.

FAQ

Which way should purlins run on an apex shed roof?

On an apex roof, purlins usually run front to back, across the width of the shed, according to Garden Buildings Direct. On a pent roof they often run side to side, depending on the direction of the slope.

Should I use nails or screws when building a shed roof?

Use screws for fixing purlins and structural timbers. Garden Buildings Direct is clear that purlins should be screwed, not nailed, to the frame. Felt is the exception: it is normally fixed with clout nails or adhesive.

Do I need to remove the old felt before re-felting a shed roof?

Many guides recommend stripping the old felt so you can inspect the boards underneath, replace any damaged sections, and start with a clean, dry, smooth deck. Check the condition of the existing covering and the boards beneath it before deciding how to proceed, and if in doubt seek advice from a shed specialist.

Can I build a shed roof in winter?

You can frame a roof in cold weather, but felting is best done on a dry, mild day. Cold felt becomes stiff and brittle, and a wet deck should never be covered, as trapped moisture causes rot.

How long should a shed roof last?

According to Shed UK, a shed roof built correctly and free of common mistakes can last 10 to 15 years or more. Quality materials and regular checks of the felt edges will help you get the full lifespan.

Final thoughts

Building a shed roof comes down to a handful of fundamentals: a square, level frame; well-fitted purlins screwed rather than nailed; flush-fitted exterior-grade boards; and felt applied from the bottom edge upward. Get those right and you will have a roof that keeps your shed dry for a decade or more. Start by checking your base and walls are level, gather your materials before you begin, and if you would rather work from ready-made drawings, free customisable plans or a plan library like My Shed Plans can save you the geometry. Happy building.

Sources

• How to Build a Shed Roof (Apex & Pent Roofs Explained)
• How to Build a Shed Roof
• How to Build a Shed Roof?