Measure the length and width of the shed. Cut two 2-inch by 6-inch wood beams to the length measurement and two additional beams to the width measurement minus 3 inches. Cut all the beams with a circular saw or similar tool.
Assemble the four beams into a box layout with all the 6-inch edges standing vertically. Connect the ends of the width beams to the inside edges of the length beams. Drive two 3-inch, self-tapping, exterior grade screws through the exterior edges of the length beams into each end of the width beams to create the box form.
Measure and place a vertical mark on each length beam every 16 inches from one end, creating matching pairs of marks on opposing beams.
Cut additional 2-inch by 6-inch beams to the width measurement minus 3 inches. Attach a beam to each pair of marks with wood screws driven through the exterior edge of the length beams into the ends of the width beams, creating the basic frame for the floor.
Attach sheets of plywood to the top of the frame with 3-inch wood screws spaced 8 inches along each vertical and horizontal beam until the entire surface is covered. Cut off excess along the exterior edge of the frame with a circular saw.
Place the flooring on leveled concrete blocks spaced every 3 to 4 feet for support. Attach the metal shed to the flooring following directions included with the purchase of the unit.