Rabbit Cage: Storage cubes, zip ties, PVC pipes to stabilize the shelves. boards to help stabilize the height of the cage. The shelves are plywood that have been varnished (so no accidents get absorbed), covered in towels secured with binder clips.
Cube type DIY cages can make for a roomy space when your space is limited. (just make sure to use the cube grids that the grid spaces otherwise, a bunny can get his head stuck in the grids spaced larger.