More obvious signs of trouble will be raised or broken shingles, a loss of mineral granules in the shingles or dark-looking spots in the sheathing. Your contractor will also check for any broken or rusty nails that have come up through the shingles. On asphalt roofs, you'll want to look for bald spots where the mineral granules have worn away. Look at the roof surface for signs of wear, checking the shingles for warping, cupping, looseness or rot. Scan the roof for any shingles that may have been lifted by the wind or are missing altogether.
Bumps can indicate that the roofing nails below have become loose.
With wood shingles, check for curled, broken, and split shingles and for spots where nails have become loose or rusted. Wood shakes show their age when wood crumbles easily between your fingers. On tile roofs, you'll want to look for cracked, broken, or loose tiles. Bumps can indicate that the roofing nails below have become loose. In valleys and in flashings around the chimney and vents, check for broken seals along the flashings' edges and for rust spots in the metal.