I think the way it works (or used to when I had my reef tank), is that the smaller aquariums have tempered glass bottoms and the larger aquariums do not because in the large aquariums the glass is thick enough. I think it is 55gallon or less that they cannot drill out the bottoms for the wet~dry filter and they have to drill the sides.
How many snakes do you have? If you are planning on only having 1 snake a 30 gallon long or 55gallon is penty. Get the 55gallon and an under the tank heater all the way to one end, thisshould cover like 30% of the bottom (a.k.a. hot end) and have nothing on the other side. This will provide for a realnice thermal gradient and the snake can pick how cold or hot he wants to be. I add in a small spot light for daytime on the hot side and a driftwood branch that they can climb up on and bask on during the day. I would put 3 hides - one hot end, one cold end and one in the middle but slightly closer to the hot end.
Many people on here advocate only small enclosures for snakes. I believe the theory is that snakes feel safer in small "holes in the ground" therefore they are better off in small enclosures ALL the time.
My experiences is that if you provide hides to make the snake feel safe it doesnt matter. Large vivariums are beautiful, more natural and I feel have many great benefits over small tubs. I have picky eaters that I have kept in small enclosures and great eaters that are in very large display tanks. It all depends on the snake. A picky eater is a picky eater. Ball Pythons are sometimes skittish - pretty much from birth. Alot really depends on the individual snake.
Many people on here keep their snakes in really, really small tubs. They do this so they can accomodate ever larger collections that take up far more space. I use a rack systems also, but I try and buy the biggest tubs possible for my larger snakes. My big girl, breeder tubs are 48" X 20"X 10".
I see nothing wrong with using a big, beautiful and very natural looking enclosure.
If people on here tell you the you should only keep your snakes in small enclosures because they prefer this and that large tanks will stress them out, this is fine, I respect their opinions. However, if I were you, I would ask myself, if what I want to do is make a nice large, natural and very beautiful eclosure, both for my visual enjoyment and for may snake to live and grow in, what is wrong with that? I would also ask myself if maybe the person who advocates only small homes for their snakes to live in might just be telling me this out of guilt? Guilt that they have rows upon rows of little plastic tubs where their snakes are unable to fully extend their bodies or stretch out all the way. They cannot climb or explore and the earth below the grip of their belly scales consists on a piece of paper towel in many cases.
Good luck with your setup, I hope it comes out beautiful and I know your snake will thrive.
~Alan