Place the 1-by-12-by-14-inch board on a work surface with the 12-by-14-inch side resting flat. This is the stool seat.
Position one 1-by-12-by-16-inch board at each end on top of the seat. These are the legs. Place the legs with the 1-by-12-inch ends flat against the seat. The outside sides of the legs should be flush with the outside ends of the seat.
Rest one 1-by-3-by-12 1/2-inch board between the legs on each side of the seat. Rest the 1-by-12 1/2-inch edges of the boards on top of the seat board. The 1-by-3-inch ends should be flush with the inside sides of the legs. These are the cross supports.
Drive two evenly spaced pan head wood screws through the outside of the legs into the ends of the cross supports with a screw gun. Turn the assembly upright.
Fasten the seat to the legs and cross supports with pan head screw every 4 to 6 inches.
Brush two coats of wood finish onto the stool with a paintbrush. Allow the finish to dry four hours between coats. Allow 24 hours after the final coat before use.