Measure and cut the boards, so that you have four 1 by 4's (at 22 1/2 inches each), two 1 by 4's (at 27 inches each), five 1 by 4's (at 20 inches each), three 1 by 4's (at 22 inches each), two 1 by 4's (at 24 3/4 inches each), two 1 by 4's (at 20 1/2 inches each), five 1 by 4's (at 21 1/2 inches each), one 1 by 2 (at 27 1/2 inches), two 1 by 2's (at 24 3/4 inches each), two 1 by 2's (at 19 1/2 inches each) and one 1 by 2 (at 22 inches).
Screw the 27-inch boards to the tops of the 22 1/2-inch boards to make the arm rests and legs. Leave a 3/4-inch overhang in the back.
Screw the 27 1/2-inch board under the overhang. Screw the board into the legs and the arm rests into the 27 1/2-inch board.
Set the two 24 3/4-inch boards on their sides parallel to each other. Fit the three 22-inch 1-by-4's inside these two boards. Screw the three 22-inch boards into the side boards, so that two are flush with the top and bottom, respectively, and one is 5 1/4 inches from the top board. This is the seat frame.
Glue and screw in the seat frame into the legs of the chair 12 1/4 inches from the floor. Leave 2 inches from the outside of the leg to the seat frame. Secure boards will be added later.
Glue and screw in the 20 1/2-inch boards to the front and back of the seat frame outside, so that the 20 1/2-inch boards are flush with the legs. Screw these into place from the inside of the seat.
Place the 24 3/4-inch boards on top of the seat frame inside the sides. Screw these in through the front legs and into the seat frame from the top. These are the seat top's sides.
Glue and screw in the seat boards (the five 20-inch boards) to the seat frame supports leaving a 1/2-inch space between the boards and the arm rests and each other.
Lay out the five 21 1/2-inch boards so that they are face down. This is the seat back. Glue and screw in the first 19 1/2-inch board 3 inches from the top of the seat back. Glue and screw in the second 19 1/2-inch board 13 inches from the top. Glue and screw in the 22-inch 2-by-2 flush with the bottom of the seat back.
Set the seat back into the seat. Screw in the 2-by-2 from the outside sides using the 2 1/2-inch screws. Screw the seat back into the back support bar.
Paint or varnish as desired.