You have about 3 options. Buy a pvc style, built your own, or buy a 55-75 gal tank. Pvc style is something like an animal plastics enclosure with many choosing a t8 size that you can insert a divider to divide the cage in half until the snake is larger. There is a thread on those.
You can build your own which is what i did. http://ball-pythons.net/forums/showthread.php?t=210213
Last is a larger tank. All of this is dependant on your budget, whether you want the enclouse to be a display in a room, and what ever else that you may have/ want to do with it in your home.
A 4th option is a rack setup. Racks are good for having lots of snakes house in a smaller over all foot print. I think though a rack has to be dedicated to the same species or snakes with really close care requirements. So one rack would be for all ball pythons. I have seen pics of a 2 tub rack on here that was pretty small and i think would work with the tubs/bins that an adult could live in. Search the diy threads on racks though cuz i have never messed with one yet