I disagree with a 41qt, far too small for an adult in my opinion. Take a look at this thread. http://ball-pythons.net/forums/showt...047#post973047
Our boas will be a year old in April, and are still in 15qt "breeders" (not the standard put in a rack size, shorter w/ more floorspace). They are getting dangerously close to being cramped. I am on spring break this week and looking for possible ways to bump up their enclosure size, but it might have to wait a little while.

My opinion is to start off no smaller than a 15qt, maybe even start in a 28qt for a baby, moving up to a 41qt as they get to be a juvenile and into a custom built/commercial cage by the time they are sub-adults. 4x2x2 minimum for boys, 6x2x2 minimum for especially large males and most females...8x2x2 preferred for all of them, but really required if you get a monster female.