Measure 5 inches along a 16 1/2 inch edge of a 17 inch by 16 1/2 inch board. Repeat from the opposite corner along the opposite 16 1/2 inch edge. Draw a line between the two marks and cut along the line.
Set the pieces from step one on their 12 inch edges, 15 1/2 inches apart. Attach a 17 inch by 5 inch board flat across the top edges. Attach a 15 1/2 inch by 1 1/2 inch support by its narrow edges under, and in the center of, the 5 inch board and screw it to the side boards.
Attach a 17 inch by 12 inch board flat to the 12 inch edge of the assembly.
Attach a 15 1/2 inch by 8 1/4 inch board as a middle step in the assembly, halfway between the 5 inch and 12 inch board. Attach a 15 1/2 inch by 1 1/2 inch support to it facing the same direction, and in the same manner, as the one on the 5 inch board.
Repeat steps one through four, but attach a 15 1/2 inch by 1 1/2 inch support under the 12 inch board, which will be part of the chair seat.
Place the first assembly on its 17 inch by 12 inch side and put the two assemblies together to form a cube. Connect the two assemblies by attaching the hinges to the 5 inch board of the first and the 12 inch board of the second, so that when the second assembly is swung on the hinges it sets on top of the first assembly.
Lay the 36 inch boards flat, 14 inches apart. Starting at the top, attach the three 17 inch by 1 1/2 inch boards across the 36 inch boards, with 1 1/2 inch between them. Attach the 10 1/2 inch boards down the length of the 36 inch boards, butted against the last 17 inch board. Attach this to the second assembly, so that the bottom edges of the 10 1/2 inch boards rest on the seat.