I sort of built a reptile room when we built our house, we've been in about 3 1/2 months. We had a study which we had to extend to meet house requiurements in our estate, it's about 6x3m. I have a few herps so basically designed the room around them. My husband is a sparky and he did all the electrical during the building process. Was fanstastic as we had access to the house the whole way through building. I could pick where to put power points, and add anything I'd forgotten at design stage. I went with carpet to help keep the room warm (we're in chilly melbourne). We had spare carpet off cuts, so I put some under my bigger heavier enclosures, and frog tank.
The insulation guys had extra left over from the external walls so they put some in the walls around the 'study/reptile' room. I had about 6 double power points spread around the room. We have a normal full size window which I chose to leave as the room is at the front of the house and would have looked funny if I'd changed it, but it's double glazed and it's a wind-out window so no one can climb in. We also had it tinted so no one can actually see inside the window now and also keeps out the heat on those bad hot days.
We have ducted heating/cooling and put a large vent in that room, so keeps really good temps, and most of the times the thermostats turn off cos it's at the right temp. It's also warm enough to keep my woodies colony happy and breeding!
I got a dust buster for xmas, and that's been my life saver when it comes to cleaning up in the herp room!! I still have a few older enclosures, but am buying one at a time new enclosures to all match, so the room looks good. I think having all the herps in one room has been great, easier for cleaning and feeding.
One thing you will need is storage space! I have so much crap, but I've been having cupboards put in the bottom of my enclosures so I have somewhere to put all the crap now!