Puzzle Bookcase

Fasten the shelves to the side of the bookcase. The measurements are from the bottom of the bookcase to the bottom of each shelf, so mark a single reference line down the side and set the staggered spacing off it.

Fasten the back to the back of the shelves and side, keeping the back outside corner flush with the back edge of the side. Nail through the back into the shelf and side edges. The back squares and stiffens the unit.

Attach the cubby sides, outside edges flush — the bottom cubby side reaches all the way to the bottom of the bookcase to carry load, the upper ones are shorter. Then fasten the footer.

Build a cubby from its top, bottom, sides, and MDF back, keeping outside edges flush. This is the module that clips onto the side bookcase.

To add cubbies, fasten them to the side bookcases with 1-1/4" screws through the shared side. Because it's tall and modular, anchor the assembly to the wall to prevent tipping. Sand and finish.