I'd say the best option for a "pet" colombian boa is a commercial plastic cage such as the ones mentioned above by Aeries. I've seen some pretty nice home-made cages as well. Male boas generally do well for life in a 4x2ft cage, while females will probably need a 6ft long cage by the time they hit the 8 foot mark.

You can also get a smaller one for your ball python (most people who keep their ball pythons in cages use 3x2foot ones), or you can go the rack route and have a couple extra tubs. A single plastic cage would be cheaper than a 3-slot cb70 rack, and a homemade cage (3x2 or 4x2) will cost about 100 bucks to build if you shop smart.