There are a lot of people doing fiberglass roofing that really haven't got a clue. Done right glass should NEVER crack in heat or sun otherwise there would be a lot of sunken yachts in the Med!
The trouble with glass is that despite some people's observations of how easy it is to lay there is actually a lot of science involved in the curing process, depending on what type of resin and catalyst you use mixing down to the mm can be very important... And yes, moisture or a shower of rain can f**k the whole job up.
Surface prep is so important, not just the material but making it dust fr