DIY Shed Foundation

Measure out the dimensions of the shed on your building site. Stake the corners and run twine to each stake. Measure diagonally, from corner to corner, with a measuring tape. The distance should be equal; if not, the foundation will not be square. Make adjustments until the diagonal distance between each corner is equal.

Dig out the site to a depth of 8 inches. Compact the soil with a hand tamper, then check the soil with a carpenter's level to ensure a flat, level surface.

Pour 4 inches of gravel over the soil. Rake the gravel to fairly level, then tamp it down with the tamping tool. Check the gravel again with the carpenter's level and make adjustments as necessary.

Measure 2-by-4-inch planks to the same dimensions as the perimeter of the shed. Place the planks around the perimeter of the prepared area, edge side up. This will be the form for your concrete. Before nailing the boards together at the corners, check for squareness by laying a 2-by-4 across the center and putting a carpenter's level on top. Make adjustments as necessary by adding or removing gravel.

Drive stakes into the ground at the outside perimeter of the concrete form. Place two stakes at each corner, then one stake every 2 feet. The stakes should be right against the concrete form. Spread form oil on the inner walls of the form to prevent sticking as the concrete dries.

Mix the concrete in a bucket or wheelbarrow according to the manufacturer's instructions. Pour the concrete into the form. Slide a length of 2-by-4 over the concrete to smooth the surface. Tap the 2-by-4 on top of the form to help the concrete settle and compact.

Smooth the surface of the concrete with a trowel once you see water starting to form on top. If necessary, place a large board over the form so you can kneel on it to reach the center of the concrete with the trowel.

Place a tarp over the concrete and allow it to cure overnight. Check the manufacturer's label for specific information on drying times before attempting to remove the forms. Depending on the product you use, the foundation may be ready for your shed in as little as a week or up to a month.