How to Plan a DIY Shed Build: Materials, Size, and What to Do First

Building your own garden shed is one of the most cost-effective DIY projects you can undertake. A well-built timber shed that would cost £1,500–£3,000 from a supplier can be self-built for £400–£900 in materials, depending on size and specification. The savings are real — but so are the mistakes that most first-time shed builders make.

The most common is starting without a plan. Buying timber based on rough estimates, discovering mid-build that lengths are wrong, and making expensive trips back to the builder's merchant is the norm when the planning stage is skipped. This guide covers what to work out before a single piece of timber is ordered.

Step 1: Decide the Size

The most common shed sizes in the UK are 6×4ft, 8×6ft, 10×8ft, and 12×8ft. The right size depends on what you are storing and how you will use it:

• 6×4ft — bikes, garden tools, small storage. Minimum viable shed.
• 8×6ft — most popular domestic size. Fits a workbench on one side plus storage.
• 10×8ft — comfortable workshop space. Room to work inside alongside stored items.
• 12×8ft and above — serious workshop, hobby room, or large storage. May require checking permitted development rules (see below).

Build bigger than you think you need. Sheds fill up faster than expected and extensions are more expensive than getting the size right first time.

Step 2: Choose Your Roof Type

Roof type affects both the visual appearance and the height, which matters for permitted development compliance:

• Pent (single slope) — simplest to build. One slope from front to back. Lower overall height. Good for sheds close to a boundary.
• Apex (pitched) — the classic shed roof. Two slopes meeting at a ridge. More headroom inside. Slightly more complex to build but still well within DIY capability.
• Reverse apex — the ridge runs front-to-back rather than side-to-side. Useful for sheds accessed from the gable end.

For most DIY builders, a pent roof is the easiest starting point. An apex roof gives more internal headroom and looks more traditional but requires cutting a ridge board and rafter pairs.

Step 3: Foundation Options

Never put a shed directly on bare ground. Without a proper foundation, the floor will rot within a few years. The main options:

• Concrete slab — the most durable option. Requires digging out 100mm, laying hardcore, and pouring concrete. More work upfront but will last decades.
• Concrete paving slabs — quick and easy. Lay on a bed of sharp sand. Level carefully. Good for most domestic sheds.
• Timber bearers on concrete pads — pour small pads at corners and intermediate points, then lay 75×75mm treated timber bearers. Allows air circulation under the floor.
• Plastic shed base grids — fast to install, no concrete, good drainage. Adequate for lighter sheds on firm ground.

Whatever you choose, get it level. A shed on an unlevel base will have racking problems and doors that do not close properly.

Step 4: Cladding and Timber

Standard sheds use 12mm shiplap or tongue-and-groove cladding on a 44×44mm or 44×69mm sawn treated timber frame. The key specification decisions:

• Cladding thickness — 12mm is minimum, 16mm gives better insulation and durability. Worth the extra cost for a permanent shed.
• Treatment — all structural timber should be pressure-treated (green/brown tinted). Untreated timber in ground contact rots quickly.
• Frame spacing — studs at 600mm centres is standard. 400mm centres for heavier loads or insulated walls.
• Roof covering — mineral felt is the budget choice but has a 5–10 year lifespan. Onduvilla or similar composite roof tiles last 20+ years and are only slightly more expensive.

The Materials List Problem

This is where most shed builds go wrong. Working out exactly how many pieces of timber you need, in what lengths, for a given shed size is genuinely complex — especially when you factor in wall framing, roof structure, floor joists, and cladding coverage.

A typical 8×6ft apex shed requires:

• Floor joists: typically 7–9 pieces of 75×50mm at various lengths
• Wall framing: 20–30 pieces of 44×44mm at various heights
• Roof rafters: 10–14 pairs at calculated rafter length (depends on pitch)
• Cladding: calculated from total wall area minus doors and windows
• Roof decking or purlins: depends on roof type
• Fixings: joist hangers, structural screws, ridge bolts

Getting one of these calculations wrong means either running short mid-build or over-ordering significantly.

Permitted Development — Do You Need Planning Permission?

In England, most garden sheds fall under permitted development and do not require planning permission, provided:

• The building is not in front of the principal elevation of the house
• Maximum height is 2.5m if within 2m of a boundary
• Total outbuildings do not exceed 50% of the garden area
• The property is not listed or in a designated area (AONB, Conservation Area)

Check these rules before finalising your size and position. A shed that exceeds them will need planning permission — or will need to be moved or reduced in size.

Build Order

Once your materials are ordered and your foundation is level and cured, the standard build sequence is:

1. Floor frame and decking
2. Wall frames (build flat, then stand up)
3. Roof structure
4. Cladding
5. Roof felt or tiles
6. Door and window fitting
7. Treatment and finishing

Plan your build sequence before starting and you will avoid the most common mistake: cladding a wall before the roof structure is in place and then having to remove it to fit the final rafter.