Master carpenter Tim Rice uses 2x6 pressure-treated lumber ($6 for an 8-foot board at home supply stores) to frame the floor. Create a 4- by 8-foot box using two 8-foot rim joists and seven 3-foot by 9-inch joists set every 16 inches on center (figure D) to which you will attach a sheet of plywood for the floor. Check each floor joist as you lay it out so that the natural curve of the lumber points up for more strength. Then fasten them to the rim joists (figure E) with 3-inch deck screws.
Set the frame on the pier blocks (figure F) and center the corners so that there's still room on the blocks to build up the shed walls.
Lay a 4x8 panel of 3/4-inch, exterior-grade plywood (about $20 per sheet) over the frame. Toe-screw the frame to the pier blocks and secure the plywood to the floor joists to complete the shed floor (figure G).
Step Two: Framing the Walls
The design calls for a flat, sloped roof, so the back wall is built taller than the front, with angled side walls. Walls with no windows or door have studs spaced 16 inches on center. Walls with a window or door need additional support.
Rice uses Douglas fir 2x4s ($1 per foot) for the back wall studs. Mark the top and bottom planks every 16 inches on center and nail on seven 7-1/2-foot-long studs. Mount the frame so that it lines up with the back edge of the floor (figure H) and secure it with deck screws.
Check that it's plumb, and then tack on a temporary brace (figure I).
Next, frame the front wall, which is 6 inches shorter than the back wall. Because it will support both a door and window, it needs extra support.
Attach planks as shown in figure J. Once it's complete, attach the wall to the flooring and add a brace to link it to the back frame (figure K).