Adopting cats can be lots of fun. But you need to make sure they are fed properly and get enough exercise on a daily basis. We have covered plenty of exercise wheels for cats in the past. You could always build your own though. bbarlowski has shared a guide that shows you how to build your own cat exercise wheel.
This modular cat wheel is made from plywood. It assembles like a puzzle into a complete wheel. Each part is CNC milled with precision. You can find more information about this project on Instructables.