Search for posts by Betrayed showing how he made his rear spoiler and fender flares or search for the pictures of the BRS Auto Design wide body development to see what's involved. Figure 200+ man hours if you know what you're doing and you might end up with something of reasonable quality. For a taste of what it takes to make composite parts check out Paul Bird's Sub 2500 lbs. 96 Mustang Cobra Project. Keep in mind that while fiberglass is easier to work with than carbon fiber the hardest part of your job will be sculpting the foam/clay/bondo to get your desired shape and then turning that into a usable mold.