We've built two so far ... mostly from leftover carpet and scrap wood. We built one free standing pole -- which is spring-loaded, and one wall-mounted climber.
The wall-mounted was the easiest to build -- neither were hard. The wall-mounted is a bigger commitment though since it is actually mounted to your wall.

You can remove it in a bind ... but not every time that company comes over, you know?
We've also built door-knob hangers which are incredibly easy to build if you need something to hold you over until you can get around to a pole.
