When I did my roof, I talked to alot of professionals. They all said, if its a wet day, great, go for it. It will keep the dust on the ground and off your car. My roof turned out well(It was my first time, gun sputtered on the last coat, and it was single stage). I talked to about 4 or 5 pros and they all said its good for it to be wet outside. Just don't let your car be wet at all.