Been offline since I first posted this message. Thanks to everyone who replied.
Ad, your new snake room looks great. . I suppose that is what I would be aiming for.
In relation to the insulation issue, my collection is currently housed in a room surrounded by double brick walls, without insulation, and the ambient temperature drops to about 15 degrees over winter, so I've never had any issues with cooling in the winter. However, even if the new shed is insulated well, I would like to have a heater/air conditioner to be able to control the ambient temp in the room and just let the thermostats in the individual enclosures do their job. Day time heat in the enclosures would be alright, but night time temps might get a bit too low without insulation.
I haven't started to price building materials and components yet, but I assumed it would cost more than the $2-2.5K people have mentioned, not including security. Now I've just got to keep working on "the boss" and try to sell the whole idea.
Rock, your setup sounds awesome, but I'd have heaps of trouble selling that idea to the missus as it sounds really expensive, she already thinks I spend too much time and money on my collection