Oh I know you have to pay almost a couple hundred dollars for anything really nice and really big. I had to use nails for the one I used floor matts for becuase they where really thick, but i used a mixture of small nails, staple gun, and hot glue for the other one. Only because I used carpet, and cloth on it. Hot glue is great for the light stuff and nails or staples for the heavey stuff(and anywhere they sharpen their nails at, that way they don't pull the carpet off while doing it.LOL)
Some really good things to use are...logs, large heavey cardboard tubes, 2x4, 4x4, and any odd things laying around, the carpet and cloth is used to ceover ALL the ugly parts, LOL or misshaps in my case. LOL
Good luck!I used boxes to make those sort of house areas too.Where they can go into and sleep or hide. Let me know how it goes!!!