We have a specific reptile room. In the summer it is not airconditioned, and stays about 82 during the day and goes down to about 74 by the early morning. In the winter we heat it to 78-80 during the day with a space heater on a timer. The space heater is timed from about 6am-6pm, and has a built in thermostat. The night drop sometimes gets down to 68-70 on the really cool nights. I live in Philly. I have had success for the last two breeding seasons with this setup.
Our reptile room is a 3rd bedroom/nursury room that is probably about 9x12" and has two wooden shelves for glass tanks, one hatchling rack, one multiple enclosure, one chest of drawers for supplies, and one kithchen cabinet and counter-top. The counter top is great for preparing food, medical evaluations, and stuff like that.
We have a couple display tank around the house and rotate our adult stock every once in a while to the family room or the office for a change.
Biggest downfall: In the summer, when it is 90 outside, it really sucks cleaning cages in 82° heat. I usually wait until later at night to clean cages to avoid the heat of mid day.
I have gotten pretty used to this setup, and when I buy my next house, I will definately be looking for a place with an extra room to keep my herps.