The durability and longevity of a shed stem greatly from the quality of the floor or base. The standard base is made out of exterior-grade plywood and treated lumber using techniques similar to building a framed floor or wall for a house. The base is elevated off the ground with levelled concrete blocks or concrete footers to prolong the life of the base. Build the base after assembling the shed to properly gauge the width and length dimensions of the completed project.
Measure the width and length of the shed along the bottom edge. Cut two 2-inch by 6-inch beams to the length measurement with a circular saw. Cut two additional beams to the width measurement minus 3 inches.
Assemble the four beams into a basic box shape with the 6-inch edges standing vertically. Drive two 3-inch self-tapping, exterior-grade wood screws through the sides of the length beams into each end of the width beams to complete the box shape.
Measure and mark the inside edge of the length beams every 16 inches, creating a pair of marks evenly spaced. The last set of marks may be closer to the end of the beams than 16 inches.
Cut additional beams to the width minus 3-inches measurement. Attach one beam centred on each pair of marks with two 3-inch wood screws driven through the length beams into the ends of the width beams to complete the frame assembly.
Place sheets of plywood on top of the assembled frame. Drive 3-inch wood screws through the plywood into the edges of each length and width beam spaced 8-inches apart. Cut excess plywood off flush with the exterior edge of the floor with a circular saw.
Place the floor on top of levelled concrete blocks or footers. Attach the shed to the floor with 3-inch wood screws through the base of the shed walls or with an anchoring kit.