If you build it...he will...be forced to live in it.

Okay, the cage is done! We had to buy some more materials, specifically:
2 2x4s
2 thinner pieces of wood (bracing for top and inner shelves)
6 casters (2 that lock)
1 extra pack of cable ties
1 set of wood screws
8 wood braces
8 connectors (sorry, I forget what they're called, but we needed 'em to connect the cage to the wheel frame)

In the end:

Harvey's new pad

Harvey hopping around the cage

Yeah, it's my place, wanna come in?

Don't mind if I get a bite to eat...

Another view of the cage, with doors closed.

Harvey going to town on his food...door lock clearly visible.

And...finally, in 3D...the cage...

This cost us about $100 to build, and about 3-4 hours effort. It's very sturdy, and can be moved around easily, has two large doors, and carpet flooring that can be removed easily if needed.