You might try Animal Plastics or one of the other reptile cage builders. I unfortunately can't be of more help.
Last year I built my own paludarium, but I needed somebody to provide the tempered glass for the doors. Just the glass, that's it. I called and visited many glass shops, only to have them either not return my calls, or treat me rudely, or flat out refuse to help my. Not lucrative enough, I guess. That's the downside of an improving economy.
You might find a local "handyman" type who might build it to your specifications for a reasonable price. If you do, my first suggestion would be to be very explicit in describing what you need, and to supervise the construction very carefully. My second suggestion would be to not pay until it is complete.