Stumped by the cost of upscale cat trees? Judy DePasse of DePurrs Persians has some great instructions on building your own. It includes tools and supplies needed, dimensions, and instructions.
It took her less than a day to build using mostly materials you can find at Home Depot or the like. Be sure you use sisal that doesn’t reek of oil, kerosene, etc. You probably won’t find that in most hardware stores. The stuff I’ve seen at Home Depot was too heavily oiled.