Ok, lets think about this logically. You state that you have 1-2 inches of water buildup after a heavy rain. Seldom ever does an area get 1-2 inches of rainfall in a single drenching. Therefore, it is logical to conclude that your collection source is substantially larger than your receiving source. I think that may rule out the sunroof. I do however think this makes the front windshield a good candidate. I think this is one of the few places on the car that would have the ability to collect and distribute that amount of water to your interior. Check your windshield gasket and surrounding areas (just below and to the side). Id bet dollars to doughnuts that is where your leak is coming from.