PAINT BLISTERS....!!!!!

I have a 1999 z-28. The other day as i was cleaning it up i noticed 3-4 paint bubbles on the roof of the car. They actually look like blisters. It looks like a clear layer is seperating from the base or color layer. What could have caused this????? The sun??, bird crap??? Thanks ahead for any answers/help.

Quite possible that the roof has been repainted?? Unless you have owned it since new, and never had it painted? If it has been repainted, could be a bad paint job.