It's at least 90% upcycled. I rebuilt the front stairs and landing on our house and used the old 4x4s for the main supports/scratching posts. I cut off the ends that had rotted and used the remaining good wood.
I purchased some pieces from a place I like to frequent called Second Chance Building Materials Center. There I found the old book shelves which I used for the napping level and two observation decks. Also, two large pieces of particle board (formerly a computer desk) for the base and landing areas, and 10 times more carpet than I needed (it was the remainder of a roll). All for $20. And I donated the remaining carpet back to them to resale.
For an unknown reason, my former employer was in possession of an old cardboard 105mm artillery shell shipping container. He was throwing it away and I knew I could make something cool out of it. I cut a hole in the top of the sub woofer and wrapped the tube in hemp rope that I purchased from Home Depot (easily the most expensive portion of the project). I attached it to the landing with a chimney pipe collar, also purchased at Home Depot. This serves as scratching post #3 and the futuristic transportation tube to-and-from the private master bedroom/sub woofer.