MAKING FIBERGLASS REAR BUMPER

I WANT TO SMOOTH OUT THE REAR END OF MY CAR BY MAKING A SMOOTH REAR BUMPER IN PLACE OF THE STEEL CHROME ONE,BUTA METALSHOP TOLD ME $600 TOMAKEONE SO THEY TOLD ME TRY TO MAKE IT MY SELF OUT OF FIBERGLASS,HOW HARD WOULD BE TO MAKE ONE?