The original design required the use of only one 2′ x 4′ piece of plywood, which kept costs and waste low. Start by planning out how all of the tiers of the cat tower would be sized, maximizing the available materials.
Planning your own? In addition to checking for carpet at the big-box stores, look for remnants at secondhand shops like Habitat for Humanity’s ReStore to get a small quantity at a discount price.
The vertical spans give the cats a secure place to scratch. The four tiers of the cat tree received a similar treatment, each wrapped individually with pieces of inexpensive carpeting and stapled securely into place to give the animals a sleeping surface that would withstand the wear and tear of cat claws.