I go to Gold's Sugarhouse gym in Utah. I've heard so much about the benefits of heat in muscle building. The Sugarhouse gym is so cold I have to wear 4 sweat shirts and 2 sweat pants. I used to go to the Lake Forest World Gym in California where the climate is ideal. What's the best air temperature for lifting weights?

Heat with muscle building? That's ridiculous. Unless that information was from a medical journal...nah, it wasn't.
If anything, it's cold that is going to help you. Your body will burn more calories in the cold trying to keep your temperature up, provided that you have normally functioning thyroid. Where temperatures are higher, you will burn calories as usual but additional sweating causes you to lose minerals that are not only for vital functions but integral for muscle contractions also. Aside from the dangers of dehydration, working out in summer heat just makes me feel considerably weaker. It's a good idea for a gym owner to keep the place cool. Think of it this way...when you're too hot there's not a whole lot that you can effectively do about it except run the AC and your electric bill through the roof. If you're a little cool...you just put some more clothing on.