I build my cages. The core is Medium Density Fiberboard with a lightly textured Melamine-type material laminated to it. Once the parts have been assembled, I run a bead of Silicone along the seams. The front openings are frames with acrylic panels that slide in tracks defined by strips of MDF or hardwood sealed against water absorption with varnish. Various vents are added and covered with screen. It's all available at my local home center, and much more economical than any commercial product--a finished cage measuring six feet long, thirty inches deep and fifteen inches tall costs about $80.00 including lights.
I think a cage of these dimensions is adequate for a female adult Bcc for most of her adult life. If she grows over 9 or 10 feet, you may need something bigger. A male Bcc ought to be able to live all his life in a cage of these dimensions.
One problem people encounter when trying to build their own cages is the purchase of the power tools needed--they aren't cheap, but if you are going to be in this hobby for a while and likely to build several cages, think about how much commercial cages will add up to including shipping, and see if it works out about even. I'm a woodworker anyway, so I had that going for me. It might not be the way to go for everybody.