Prepare the Area and Lumber
Determine the location and position for the sandbox, then spray-paint the outline on the ground. This sandbox measured roughly 4 feet by 8 feet; adjust dimensions as needed for a different sandbox size.
This project utilizes redwood lumber. Cedar can also be used. As a space for children to play in, you don't want to use treated lumber that hasn't been thoroughly dried, sanded to remove all possible splinters and painted with non-toxic primers and paints.
Cut frame lumber. Measure and cut a 4-foot length from each of the 2x12s. This will yield two 4-foot-long pieces and two 8-foot-long pieces.
Cut post lumber. Cut six pieces of 4" x 4" post, each 10 inches long. These will serve as the corner supports for the sandbox and will also support the lid.