To build a shed foundation, dig a 6-inch deep trench supported by wooden inserts, and layer the trench with crushed gravel, sand and concrete. You need a tape measure, stakes, string, a garden spade and a tamper.
- Outline the base
Outline the base with string tied around four stakes. Ensure the area of the outline is 2 inches larger than the actual dimensions and is squared diagonally.
- Excavate the area
Excavate the area to a depth of 6 inches. Tamp the area with the flat side of a garden spade until it's flat and level.
- Install a wooden outline
Cut four 2-inch by 4-inch boards to the dimensions of the outline. Remove the stakes and string, and install the boards along the edges.
- Add a compacted base
Pour a layer of crushed gravel in the area, and flatten it with a tamper. Do the same with a thin layer of sand.
- Pour in the concrete
Mix a small amount of the concrete according to manufacturer instructions. Pour the concrete along the width of the base and over the lumber supports.
- Build a concrete layer
Use a piece of lumber longer than the width of the area to flatten and smooth the first bit of concrete. Continue to mix, pour and flatten the concrete to finish the layer.