Vision enclosure...what dimensions??

My male BP is currently 800g in a 20gL. He grew up in tubs and I'd really like to get back to the opaque sides/ lighter weight/ better humidity control theme...but still be able to watch him.
I really like some of the cages I've seen from boaphiles and vision. The next enclosure I move him to will be his final "adult" enclosure. These manufacturers give dimensions not volumes. So...what dimensions are ok for an adult male BP? I understand the L+W idea but I'm not sure of his final adult length. I don't want it to be too small, but I obviously don't want to large of and enclose to stress him out.
Here are some of the vision options :

http://lllreptile.com/store/catalog/...ages-and-tubs/

Thanks:)

I have my adult bps in the v332 model, 36x28x18. They have plenty of room to roam around but looking back now I would have bought from Animal Plastics just based on the price factor. But all in all, the Vision product is good.

Thanks for the heads up...I'll check out the other manufacturer.
If I had the tools and was remotely good at carpentry I would try making an enclosure myself :)