I've used a variety of benders for all the different radius bends needed for the birdcage. Mostly, I've used electrical conduit benders for the larger radius bends, going just a little bit at a time until they fit the body. The tighter radius bends I used an electrical "hickey" for bending rigid conduit. There are a few bends-like the door, trunk, and hood hoops that require a very tight bend. For that I bought a Harbor Freight hydraulic bender and had to bend very carefully to keep from kinking the 3/4" DOM pipe I used.
Basically, whatever is handy is what you will need to use. I'd love to have a roller bender, but just isn't in the budget this month.
Bob