Enclosure Size Dilemma's

[Wrath]

If you can give me some advice I would really really really appreciate it. My roommate will not let me put my pets anywhere other than in my bedroom, so I'm really stuck for space!

I wanted to ask you guys about tank sizes, and I'm sure no one wants to hear this redundant conversation on the forums, but I'm really hurting for some educated opinions! I am in a bit of a dilemma because I am trying to figure out what to do about my current set up, and what to do about getting another habitat in the same room.

(in inches)
What is the smallest (and most considerate) size enclosure for a rosy boa?
What is the smallest (and most considerate) size enclosure for a ball python?

I currently have my rosy boa in a tank that is 36Lx12Wx12H. Can I move him into a smaller one, say 24Lx12Wx12H? And put the ball in the bigger one??

Or should I just get a bigger one for the ball, and keep the rosy where he is? As I said I am really stuck on space....I have a tank that is 36Lx18Wx18H, but it's in storage, and I have to figure out what to use as a stand! Dilemmas!

I have a feeling that my Rosy is spoiled in that sized tank, but I seriously dont have a problem spoiling him, and I also don't want to put him on the back burner by downsizing his home.

I found this ball python for sale in my area, and the current owners are keeping her in a 20 gallon tank, in my opinion that's too small for a full grown, but what do I know? I have not gone to see her yet, so I don't know how big she really is...