Measure and cut four 2-by-4-inch boards that are 6 feet long.
Measure and cut six 2-by-2-inch boards that are 12 inches long.
Lay two of the 2-by-4-inch boards on the ground, 12 inches apart on the outside edges. They must be parallel to each other and resting on the 4-inch sides. Measuring from one end, place three 2-by-2-inch boards perpendicularly on the 2-by-4-inch boards at 24 inches, 48 inches and even with the other end. Nail the boards together with two 10d nails at the points where they intersect.
For the narrow shelves, go to Step 5. For the wide shelves, cut three 4-foot-long pieces of 1-by-12-inch board. Raise the frames upright that you built in Step 3, with the open end down, and the 2-by-2-inch boards facing in. Place the 4-foot boards onto the horizontal 2-by-2-inch boards, and nail them in place with 6d nails.
For the narrow shelves, cut three 2-foot boards, and then complete the construction by following the method from Step 4.