How can you tell if you need a new roof?

the first sign would be a leak in the roof that is visible from the interior or under roof eaves, etc. depending on the type of roofing material: aspalt type shingles should have the roof granules in place and should not be curled or cracked, wood shingles should be flat. if a few shingles are damaged, they can be replaced on an individual basis. if larger areas are damaged then the hole roof or the exposure should be replaced.