MILL & MERCHANTLEARN · PLAN · BUILD

Project tools

Shed & Outbuilding Planner

Type how big the shed is, pick a door and a roof, and get a list you can take to the timber yard.

Related guidesSpecies data
The numbers update as you type. You do not need the trade names. Type the size, choose a door and a roof, and take the list to the merchant. The person on the counter will know the rest.

Quick start

  1. Measure the outside of the shed: how wide, how deep, how tall the walls are. Use millimetres — a tape shows them.
  2. Leave the wall uprights 600 mm apart unless someone has already told you closer.
  3. Leave the usual garden-shed door unless you already have a different one.
  4. Pick a roof with a ridge, or a roof that slopes one way. Then felt on wooden sheets, or corrugated sheets.
  5. Copy the list or print it. That is what you show at the timber yard.

What each thing means

How wide / how deep
The outside of the shed on the ground. Four walls, square corners, no rooms inside. Width is across the front. Depth is front to back.
How tall are the walls
From the floor up to where the roof starts. 2100 mm is a usual start. If the roof slopes one way, this is the low side.
How far apart are the uprights
The posts in the walls. 600 mm apart is the usual garden shed. Closer (450 or 400) means more timber and a stiffer wall.
The door
A usual UK garden-shed door is about 762 mm wide and 1981 mm tall (roughly 2 ft 6 in). The hole is taken off the wall boards, and a piece of timber sits over the opening.
The roof
A ridged roof has two slopes that meet at the top. A one-way slope is higher at one side. Felt on wooden sheets is the usual garden-shed roof. Corrugated sheets are the other honest choice.
Extra for cuts
A bit extra so offcuts and mistakes do not leave you short. 10% is a fair first shed. Raise it if there are lots of corners.

The size

How big is the shed?

Measure the outside, on the ground. Width is across the front. Depth is front to back. Height is the walls, up to where the roof starts.

How far apart are the wall uprights?

600 mm is the usual garden shed. Closer means more timber and a stiffer wall.

The door

How many doors, and how big?

Leave the usual garden-shed door unless you already have a different one. The hole is taken off the wall boards, and a piece of timber sits over the opening.

The roof

Ridged, or sloping one way?

This is what to buy for the roof, not a truss drawing. Felt on wooden sheets is the usual garden-shed roof. Corrugated sheets are the other honest choice.

How far apart are the roof timbers?

What to take to the timber yard

Wall uprights to buy

19

Buy 19 wall uprights, 18.48 m of top and bottom rails, and 7.02 m² of felt on wooden sheets for a 2400 × 1800 mm shed with a ridged roof and one 762 × 1981 mm door.

18 uprights around the walls − 1 for the door + 10% extra for cuts → 19 to buy

Top & bottom rails

18.48 m

Lengths on the rack

6 × 3.6 m or 4 × 4.8 m

Roof timbers

8 @ 1442 mm

Roof covering

7.02 m²

Wall boards

18.59 m²

Overlapping boards

78 pieces

Timber over the door

1 × 1062 mm

One piece a little longer than the door. Check it at the yard — this is not a designed beam.

This is a shopping list to take to the timber yard. It is not a building design, and it does not replace Building Control.

Take this with you

Copy the list, share the job, or print a sheet for the timber yard.

What to buy

  • 19 wall uprights (ask for studs), about 2006 mm, 47 × 75 or 47 × 100 CLS, 600 mm apart
  • 18.48 m top and bottom rails (ask for plates) — 6 × 3.6 m, or 4 × 4.8 m lengths of 47 × 75 or 47 × 100 CLS
  • 1 × timber over the door (ask for a lintel), about 1062 mm — typically a 47 × 100 or a pair. Check the opening at the yard
  • 8 × roof timbers (ask for rafters), about 1442 mm, 600 mm apart
  • 1 × ridge piece, about 2200 mm
  • 3 × wooden roof sheets (OSB or boards) to cover 7.02 m² (2440 × 1220 sheets)
  • Roofing felt to cover 7.02 m² — allow extra for overlaps when you pick the roll
  • 18.59 m² wall boards after the door, or about 78 × 125 mm overlapping boards, 2400 mm long
  • About 221 framing nails, 234 cladding nails, and 57 felt nails — a 2.5 kg box of 75 mm galvanised plus a box of clouts or screws is a fair garden-shed start

In plain English

  • Outside size 2400 × 1800 mm, walls 2100 mm tall, uprights 600 mm apart.
  • 18 uprights around the walls — extra ones at the corners. 1 come out for the door. Buy 19, each about 2006 mm long.
  • Top and bottom rails: 16.8 m around the shed, 18.48 m to buy after extra for cuts. That is 6 × 3.6 m, or 4 × 4.8 m lengths — pick what is on the rack.
  • One 762 × 1981 mm door: 1.51 m² taken off the wall boards, and 1 piece of timber over the opening, about 1062 mm long. Check it at the yard — not a designed beam.
  • ridged roof at 15°, sticking out 200 mm past the wall: 8 roof timbers about 1442 mm. One ridge piece about 2200 mm. Covering 7.02 m² of felt on wooden sheets.
  • Wall boards 16.9 m² after the door (walls plus 0.77 m² extra at the pointed ends). About 78 × 125 mm overlapping boards, 2400 mm long. Run the cladding estimator if you want a different look.

Useful Mill & Merchant reading

Read before you order

A few timber lessons that sit behind a shed that stays square.

Buying timber before you build

Moisture, flatness, and what to check at the rack before you load the van.

Designing for wood movement

Why a garden building still needs room to move once it is up.

Cladding a garden room

Membrane, battens, and the details that last longer than the first summer.

Want a board count for a different profile? Run the cladding estimator on the wall area above.

Get better results

  • Timber yards sell long pieces in 3.6 m and 4.8 m lengths. The list shows both — pick what is on the rack.
  • The timber over the door is one piece to buy, a little longer than the door. Check it at the yard. This tool does not design a beam.
  • Felt on wooden sheets means boarding, then roofing felt. It does not invent tiles or slates.
  • Wall boards here are ordinary overlapping feather-edge. If you want a different look, run the cladding estimator on the wall area.
  • Use outdoor nails or screws. Take the list to the merchant and confirm lengths before they cut.

Reading the numbers

The big number is how many wall uprights to buy. Then top and bottom rails, roof timbers, covering, and wall boards after the door. The printed list uses the names the timber yard uses, so you can read it out at the counter.

Not a substitute for structural sign-off

This is a shopping list to take to the timber yard. It is not a building design, and it does not replace Building Control. It does not do wind, snow, foundations, or Building Control. If the shed is large, close to a boundary, or going to be lived in, ask before you build.