I assume you mean tub size?
I move my bps up from 8qt to something around 12-16qt to something around 28-32 qt. When I get some females big enough, I'll probably get something bigger for them, but most people seem to think 32qt is the biggest a male ever needs. I've even seen some say 32qt is the biggest they use for any BPs, but I have wondered if they just don't have any really big females. I have one girl that is about 1800g, and I just can't imagine a snake twice that big in that size tub, especially not with a male in there too for breeding.