This article explains how to build a medium sized sandbox, out of wood, for children to play in. It is a moderately easy project and is fairly inexpensive.
Choose what type of wood you want to use. Chemically treated wood is not suggested. Untreated spruce, fir or pine are excellent choices.
Cut the wood to size. You will take two pieces of 2X12 inch lumber and cut them into 3 foot, 10 1/2 inch lengths. Take two more pieces of 2X12 inch lumber and cut them into 4 foot pieces. Cut four pieces of 4X4 inch lumber into 11 1/4 inch lengths. Then cut four pieces of 3/4 inch plywood into trianges with the sides equaling 15 inches and a 90 degree angle (optional). Finally cut one piece of decorative lattice into 4X4 foot square (optional).
Assemble the frame using the 2X12 inch lumber. The shorter pieces will be used for the sides and the longer pieces for the front and back. You will secure all the pieces with the 3 inch nails at the corners.
Brace the corners using one 4X4 inch block per adjoining side. If done correctly, it will create a 90 degree angle and secure each angle with three nails on each side of the block.
Create seats if you choose. Corner seats are a nice touch. To do this, install the triangle pieces, that you previously cut, to the corners of the sandbox to form seats.
Use lattice to cover the box. This step is optional. If you chose to use the lattice, cut it into 4X4 foot size, and use this as a cover for the sandbox when it is not in use.