Enclosure size?

Okay so my brother has a boa that I have been trying to get for sometime and he finally said okay that i can have him. He is four years old and right at 5ft. I'm going to take him. However this poor snake is currently living in a 20g long tank. With a high temp of 75degrees. :( obviously my first order of business is to get him a much larger home and proper temps. But what size should I go with? He will be my first snake and I'm simply not well versed on cage sizes for them. Lol. Can someone give me dimensions for an ideal enclosure for his size now and for when he is full grown. Now I know it will be large and perfectly fine with that. My water dragons have an enclosure that spans an entire wall (8'Lx4'Hx2'W.
Anyways any help would be appreciated. Thanks...

20g tank? I don't even keep my 6" Leopard gecko in a 20g tank!

I'm not experienced with boas, but frankly, anything larger than that would be a good alternative compared to how he is living now. Heck, even a temporary large rubbermaid tub would do the trick until you get an enclosure figured out. At $10-$15 for one, it'd be an upgrade for that guy. For sure.

I wouldn't put him in anything smaller than a 4' x 2' x 2' (L x W x H) cage. I would put him in a 6' x 2' x 2' personally. I highly recommend PVC cages as they hold heat and humidity in far better than tanks.

http://www.animalplastics.com

Their T12 (4' x 2' x 2') or T20 (6' x 2' x 2') would be perfect.

Here is a thread I wrote on these cages: http://ball-pythons.net/forums/showt...With-Pictures!