How to Build a Strong Shed Floor

Clear the shed site, rake it smooth and fairly level and set concrete blocks for a foundation. Set blocks on top of the ground or into the ground as necessary to level them. Put one block at each corner, one in the middle of each wall and one in the center of the shed. Space them for the size of the shed, 8-by-10-feet, for instance. Set them with the open edges up. Measure from corner to corner with a tape measure and adjust the blocks until those figures are the same to square them.

Build a frame for a shed floor with 2-by-4-inch framing lumber. Use front and back bands the full width of the shed -- 8 feet, for instance -- but cut the side bands with a circular saw to allow space for the ends; 9 feet 9 inches for 10-foot length, for instance. Nail the end bands to the side bands with 16d framing nails and a hammer. Use a framing square to make the corners square and double check with diagonal measurements.

Set the frame on the blocks and use it to fully square the foundation. Rest the frame on the outside edges of the blocks and level it with a long board with a level on it. Adjust the base under the blocks to get the frame level in all directions. Make sure the frame is solid on the blocks and doesn't wobble.

Cut 2-by-4 joists to fit between the two side bands, allowing for the width of the bands; that would be 7 feet 9 inches for an 8-foot shed, for instance. Use metal joist hangers to secure them. Nail the hangers to the side bands, set the joists in them and nail them in place. Put the first joists on each end 23 1/4 inches in from the end and space the others with centers 24 inches apart.

Cover the floor with 3/4-inch plywood, preferably with tongue and groove connections between panels. Lay plywood with the grain running across the joists. Install as many full panels as possible and cut other panels to fit with a circular saw. Offset partial panels so the seams of the panels don't align. Fasten the panels with 8d galvanized nails or 1 1/2-inch galvanized screws, driven with a screw gun.