Cut the lumber to the correct dimensions using a power saw. If you don't have a power saw, ask your lumber yard to cut the lumber for you.
Drill a pilot hole through each corner of the lumber sheet, positioned 1/2 inch from each edge. Drill a corresponding pilot hole 1/2 inch deep in the 1-inch wide side of both ends of each 48-inch strip, on center 1/2 inch from the end of the strip. Use a drill bit 1/8 inch narrower than the diameter of your screws.
Drill two pilot holes in each end of the 34-inch strips using a drill bit 1/8 inch narrower than the diameter of your screws. Position the pilot holes on center, each 1/2 inch from the edge.
Drill two pilot holes at each end of both 48-inch strips using the same drill bit as in step 3. Drill all the way through the face of the strip, 1/2 inch from the end. Position each hole 1/2 inch from the edge of the strip.
Sand all surfaces of all pieces of lumber.
Assemble all four strips into a rectangle with the ends of the shorter strips abutting the faces of the longer strips. All four strips should rest on their narrowest face.
Connect the rectangle by driving wood screws through the pilot holes in the long strips and into the pilot holes in the short strips.
Lay the lumber sheet on top of the rectangular frame. Connect it by driving wood screws through the pilot holes in the sheet and into the pilot holes in the strips.
Set one post on end in the corner formed by two of your strips. Attach it to the plywood sheet by driving two wood screws through the plywood and into the end of the post. Reinforce by driving two screws through the face of each strip and into the side of the post.
Repeat step 9 three times to mount the other three legs.
Add additional components, paint and features according to your customized plan.