I just built a wooden enclosure that measures 36"x24"x18" its pretty huge and i think a great size for a full grown ball.
I'll post some pictures when i figure out how.

But i think that just because some breeders keep their snakes in a certain size tub doesnt mean that it is the size you should use. They have many snakes and need the perfect size tub for room space and snake space. If you only own a one or two snakes then i think that a bigger size enclosure would be better since they are your beloved pets and not products to sell.