Saw 4-by-4-inch lumber into two pieces approximately the height of the seat you want. Cut another two pieces that measure twice as long, enough to support your back. The finished dimensions of each leg should be 3 1/2-by-3 1/2 inches.
Measure 1 1/2 inches of depth into the back legs and cut downward, stopping at the level where the seat should be. The finished legs should be thinner on the top half and thicker on the bottom half.
Cut 2-by-4-inch lumber into four boards long enough to extend from leg to leg, forming a square with the legs in the corners and one board long enough to extend from the back board to the front board, forming an “I” shape. These boards form the base support of the seat.
Trim a sheet of 3/4-inch-thick plywood into a piece the size of the seat you require and a piece to extend across the back of the chair. Using a saw, router or power sander, round off the edges of the seat to a radius of approximately 2 inches.
Screw the frame and legs together, using 4-inch screws placed through the front of the front legs and the back of the rear legs, penetrating the boards on the other side. The frame needs to be at the top of the front two legs and flush with the seat of the rear legs. Use the same screws to secure the center support board through the front and back of the frame.
Screw the seat into place vertically from the corners into the legs. Screw the back panel on the top of the rear legs, using 3-inch screws.