I wanted a dice tray with tall sides that I could put in my bag or binder without taking up as much room as a textbook, so I made one that folds up and snaps together. There is a rectangle and square version, both use the same ends, and both have a version of the base cut in half. The rectangle version will need at least a 220mm bed, but the sides and half-bases should just fit on a 200mm bed if you orient them at a 45deg angle. The square version will need a bed larger than 160mm.

This is designed to use eight 16mm long M3 screws. 20mm are what I had on hand, so if you have longer screws a 7/64 inch drill is perfect for drilling out the holes in the base. The studs on the ends can be cut off and holes can be drilled in their place and in place of the indents in the sides for gluing in 1/8" magnets if you so desire. You could similarly attempt to replace the screws with magnets.