Plans for building a sandbox typically include building the sandbox frame, cutting out the bottom and the cover, attaching bottom braces, attaching corner braces, adding handles and filling the sandbox. Specific plans for building a sandbox depend on the size of the sandbox being built.
Once the size of the sandbox is determined, cut the four sides from 2-by-10-inch boards. Attach the boards at the corners by drilling pilot holes and using 3-inch galvanized decking screws, making sure to face the smoother side of the boards outward. The bottom and the cover should be cut out of pressure-treated plywood that matches up with the size of the sandbox. Attach the bottom to the frame with 3-inch screws. Three bottom braces should be cut from pressure-treated 2-by-2-inch boards that match the length of the sandbox. Attach one at each end and one in the middle of the sandbox.
Cut four 90-degree triangles from pressure-treated 2-by-10-inch boards. Use screws to attach one to each corner of the sandbox. Cover handles can be made from a length of marine-grade rope strung through holes made 6 inches apart in the cover. Knot the rope to prevent it from sliding through the holes. Finally, fill the sandbox with sand.