Old game boards are another great thng to make book covers from. Monopoly Junior is perfect as the (open) board is rectangular so folds into a 25cm square, which is a good sketchbook size. The Cleudo boards are individual 6 inch room boards which presumably can be arranged in any order to make the full board. As they are, they are a perfect size to make a small notebook. I have only used one board for the front cover & covered a piece of plain board for the back.