Cut four 3-foot pieces from the 2-by-2s with the circular saw for the legs.
Cut eight 7-inch pieces from the 2-by-2 boards.
Cut a 10-inch square piece from the plywood.
Draw a 1-foot-4-inch square box on a piece of plywood. Mark the center of this box by lightly tapping a nail into the plywood. Tie one end of the string around the nail and extend it to the center of one of the edges of the box. Take a pencil and use the spot of your string exactly at the edge to draw a perfect 1-foot-4-inch-wide circle on the plywood. Use the keyhole saw to cut out the circle from the plywood.
Sand all rough edges off the cut pieces. Apply wood stain or paint of your choice and allow to dry.
Lay two leg pieces on the floor parallel to each other 7 inches apart. Place a 7-inch-long piece between the legs on one end so you have three sides of a rectangle. Drive a 2½-inch screw through the side of both legs into the ends of the shorter piece.
Place another 7-inch piece between the legs 2 feet away from the other 7-inch piece. Screw it to both legs with 2½-inch screws.
Repeat steps 1 and 2 and build another similar section using the other two legs and two more shorter pieces.
Lay the two sections on the side of one leg parallel to each other 7 inches apart so the 7-inch pieces are vertical. Screw the remaining four 7-inch 2-by-2 pieces between the legs not attached yet at the same level as the other four 7-inch pieces. You now have four legs with a square frame holding them together at the top and another square frame two feet below that one.
Place the 10-inch square piece of plywood on top of the frame at the top of the four legs. Drive a 1½-inch screw through each corner into all four legs.
Center the 6¾-inch swivel plate on top of the square piece and attach it. Use 5/8-inch screws and drive them through the bottom part of the plate into the plywood.
Center the round seat on top of the swivel plate. Screw it to the plate with 5/8-inch screws.