Ok. First off, my BCC Suriname is 4 years old and is smaller than most of my three year old BCI's. So, don't believe too many tales of True red tails reaching so much bigger than Colombians. It's all a possibility. That said, something along the lines of this should suffice for almost any BCI or BCC...

422D

This is plenty big enough and will give you enough head room to add in any ornaments you'd like to add in (branches, hides, etc). This is a boaphile, but there are others out there just like this. Animal plastics makes a similar one too. My opinion is there is nothing that beats a Boaphile Cage, but some would say otherwise...lol. It's all in opinion.