A 10×12 shed is the size most backyards are crying out for. At 120 square feet it's big enough for a riding mower, a workbench, and a wall of shelving, but small enough to build yourself over a few weekends without heavy machinery. This guide walks through the whole build — foundation to finishing — in the order you'll actually do it, and points you to a free, itemized material list so you know exactly what to buy.
We don't sell sheds or materials, so nothing here is trying to upsell you. The goal is simply to help you build a solid shed once, correctly.
Before you start
Two things save more headaches than anything else: a plan and a permit check.
Check the rules first. A 120-square-foot shed is right at the size where many jurisdictions start requiring a permit, and local codes also care about height, setbacks from property lines, and how the shed is anchored. These rules genuinely vary from town to town, so a five-minute call to your local building department before you buy lumber can save you from tearing something down later. Treat everything here as general guidance, not code advice — see our disclaimer.
Pick a good spot. Choose level, well-draining ground, ideally not the lowest point in the yard where water collects. Leave room to walk around the shed and to swing the door open fully. Orient the door where you'll actually use it.
Step 1: Build the foundation
Your foundation choice sets the tone for the whole build. The common options, from simplest to most permanent:
- Gravel pad on skids — a compacted gravel bed with pressure-treated 4×4 or 4×6 skids on top. Affordable, forgiving, and a favorite for DIY sheds.
- Concrete deck blocks — precast blocks that support the floor frame. Quick to level, no pouring.
- Concrete slab — the most permanent and level option, and often the most work and cost.
Whatever you choose, get it level and square. Measure the diagonals of your foundation rectangle — for a true rectangle, both diagonals are equal. Time spent leveling here pays off at every step above.
Step 2: Frame the floor
On top of the skids or blocks, build the floor frame: two rim joists running the length, with joists in between at 16 inches on-centre, all sitting on the supports. Use pressure-treated lumber for anything close to the ground.
Once the frame is square and level, sheath it with exterior-grade plywood or OSB to create the floor deck. This deck becomes your work surface for framing the walls, so make it flush and solid.
Tip: Frame and sheath the floor as one flat, square platform before you stand a single wall. Everything above is only as straight as the floor beneath it.
Step 3: Frame the walls
This is where a 10×12 really takes shape. Walls are typically built flat on the floor deck, then tilted up into place.
Each wall is a bottom plate, vertical studs, and a top plate. Standard practice for a shed like this:
- 2×4 studs at 16 inches on-centre for a stiff, well-supported wall.
- 3-stud (California) corners, the modern standard, which give solid backing for siding and any interior finish.
- A double top plate to tie the walls together and carry the roof.
- Extra studs framing each door and window opening.
Build each wall flat, check it for square, stand it up, brace it, and fasten the bottom plate to the floor. Then tie the walls together at the corners and add the second top plate.
Not sure how many studs and boards that adds up to? Our Shed Material Calculator counts it for you — for a standard 10×12 with 8-foot walls, 16-inch spacing, 3-stud corners, one door, and a 4/12 roof, it estimates about 54 studs plus plates, and shows exactly how it got there.
Step 4: Build the roof
For a 10×12, a gable roof is the classic choice — two sloping sides meeting at a ridge. The roof pitch (how steep it is) affects both the look and how much material you need, since a steeper roof has more surface area than the flat footprint below it.
Cut your rafters to match your chosen pitch, set them in pairs against a ridge board at the same 16-inch spacing as the walls, and make sure the overhangs are even on both ends. If your span or snow load is on the heavier side, step up from 2×4 to 2×6 rafters — when in doubt, ask a local pro or your building department.
Step 5: Sheathe and side the walls
With the shell framed, cover the walls. Panel siding like T1-11 comes in 4×8 sheets and doubles as both sheathing and finished exterior in one step, which is why it's so popular for sheds. Alternatively, sheathe first and add lap or board-and-batten siding over it.
Work from a corner, keep sheets plumb, and cut openings for doors and windows as you go. Add house wrap or a weather barrier if your siding calls for it.
Step 6: Roof it
Install roof sheathing over the rafters, then your roofing. Asphalt shingles are the most common and DIY-friendly choice: they're sold by the "square" (100 square feet), with roughly three bundles per square. Don't forget drip edge and underlayment — the details that keep water out for the long haul. Metal roofing is a durable alternative if you prefer it.
Step 7: Doors, windows, and finishing
Hang your door (single or double, depending on whether a mower needs to fit), install any windows, and add trim and corner boards. Finish with paint or stain to protect the siding. A little caulk at the seams and around openings goes a long way.
Your 10×12 shed material list
The fastest way to avoid a second trip to the store is to shop from an itemized list. We've pre-calculated one for this exact size:
- See the full breakdown on our 10×12 shed material list — studs, plates, rafters, siding, sheathing, and shingles, with a 10% waste factor already included.
- Building a different spec? Open the Shed Material Calculator to adjust wall height, stud spacing, roof pitch, and openings, then copy or print your own list.
Remember that these are planning estimates. Always verify quantities against your final design and current product sizes before buying, and add a waste allowance for cuts and mistakes.
Common mistakes to avoid
- Skipping the permit check. It's the step people regret most.
- A foundation that isn't level or square. Every error here multiplies as you go up.
- Under-buying materials. A 10% waste allowance keeps you from stalling mid-project.
- A door too small for your biggest item. Measure your mower or trailer before choosing door width.
- Forgetting the "extras." Fasteners, drip edge, house wrap, hinges, and trim aren't in most framing counts — budget for them separately.
Build it once, build it level, and a 10×12 shed will serve you for decades. When you're ready to shop, start with your material list — and since we don't sell sheds, you can trust the numbers are just numbers.