I have a 3 ply mop down flat roof (3 layers of glass felt, mopped down with asphalt and pea gravel layed on top). The roof has a leak that is getting worst quickly. The roof is at least 20 years old. Should I replace the entire roof, or attempt to repair it, or maybe even consider pitching the roof? I understand that pitching the roof will involve much construction but if I pay for a replacement roof that has to be replaced in 12-15 years, I'm thinking that pitching the roof should at least be considered. The flat roof is about 360 sq feet.