I really like the Boaphile cage we have. The swinging door can be kind of a pain though cause it swings down and I'm afraid I might break it off if I bump it. Animal Plastics and PVC Cages also make some nice ones. I think when I get our boa his new cage I will go with AP, they have a 6' one that I like (the T25 model w/sliding doors). They can be heated with flex watt or a RHP. As far as size, I'd go with the biggest size you can afford. Unlike Balls, Boas do fine in big spaces. Our little guy will be in a 2x2x1.5 as soon as he's out of QT and he is TINY. He'll have a few different hides and branches to keep him happy in it.