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:
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.