adult enclosures

What is the best size to build an enclosure for an adult boa? I was thinking 6 feet long by 4 feet wide by 4 or 5 feet tall.

That will end up being a really large area to try and keep heat and humidity at the right levels. A 4x2x1 enclosure is plenty big for most adult BCI, with some larger animals requiring a 6x2x2.

Yep, stay away from the very TALL enclosures for boas. The heat will rise up to the top while the boa will mostly stay at ground level (when they get older, some like to climb more when young), so the ground level won't be warm enough. It'll cost you a LOT of money to try and heat a cage like that.

It's one thing if you want to make a large display cage for one boa, and can dedicate yourself to the extra cost and upkeep such a tall cage would create, but most people who have lots of snakes find that short, wide cages are the easiest and most effective. That, and the fact that most adult boas will not UTILIZE the tall space leads many to go towards shorter cages.

So, all of that to say that I agree with Randall.

So if 4 feet is too tall and I dont like the idea of only 1 foot tall, would 2 feet be ideal?
It just doesnt seem right to put that large a snake in an enclosure with that little head room. I appreciate the opinions and I also appreciate that you guys probably have far more experience than I do, what about something around 5x3x2?

I have a 5' long x 2' deep x 2' high cage that came with a couple of rescues. I keep an 8.5' surinam in it, and she does fine. She never sticks her head up towards the top of the cage, so 18" might be sufficient. The only problem I have with that cage is that it is wooden and so I can't heat it with flexwatt like most of my other cages - I have to use the ceramic heat element (the person who built it made a hole with hardware cloth to house the fixture above the cage), but that heats it just fine.

I hope this helps! It really all depends on what is most important to you. Some people are fine with plastic tubs, some want high-end cabinet-quality display cages, and some people make do in between.