A fiberglass roof is made up primarily of two products, a glass material and a resin. The resin is subject to UV degradation. The white colour reflects more than the darker colours, but after time, it will become damaged. This can be verified by wetting your finger and rubbing it over the roof's surface. If this results in a white powder on your finger tip, the resin is damaged.

This is very common in marine environments, where, even though most of the boats are finished white, the extreme exposure to the sun light and reflectivity of the water, combine for major problems. There are specific products that will remove the dead, oxodized resin and provide a new looking surface, while offering some future UV protection. The waxes are not particularly long lasting, as weather will eventually wash them away, and your efforts will have to be repeated.

Once the resin is damaged, the best and easiest protection is the application of a paint product. A marine paint has a high solids content, excellent coverage, good UV reflectivity and durability, and will protect your roof for many years. Other than the masking, it isn't much more work to recoat, than it is to wax and buff the whole area, and then do it again, and again.....

If the roof is not exhibiting any resin failure now, it usually will start within 5 or 6 years from new. If left unchecked, the resin will no longer support the glass fibers, and the roof will become flexible, most likely develop cracks, and will eventually need major repairs. The amount of time in which this will occur, depends on the OEM materials and your specific weather conditions.

Here are many brands of waxes for fiberglass:

http://www.jamestowndistributors.com/userportal/search_subCategory.do?categoryName=Waxes&category=622&refine=1&page=GRID