I bought a bike on E-Bay from Arizona. I'm guessing it had been in a garage for about fifteen years. No rust. But, the "solar heating" of the afternoon sun must have gotten that garage up to some astounding temperatures. All of the grease in the headset had "boiled out" and its residue dried on the headtube. Likewise, the grease in the wheel bearings. The plastic fittings were brittle and cracking.
So, if the garage has a "cool" side and a "hot" side, you really want to hang it up on the cooler side.