It’s recommended for homeowners to do a roof inspection at least twice a year (spring and fall).The best place to begin is in your homes attic.
When in your attic here are a few things you should look for:
1) interior sagging of the roof.
2) signs of water damage or leaking
3) Dark spots
4) Outside light shining through the roof.

After you thoroughly examined for the above you are now ready to move on to the exterior:

5 ) Visually inspect for your roof for broken, torn , bald or missing shingles.
6) Scan the roof for loose material or wear around chimneys, vents , pipes or other penetrations .
7) Look for an excessive amount of shingle granules in the channels ( this is a sign of advanced deterioration).
8) Check for signs of moisture , mold or mildew. (wet stains can travel directly under your defective shingle, water will travel to its lowest point before it drips . Mold, fungi and bacteria can grow as quickly as 24 to 48 hours after a water problem).
9) Check the drainage, and make sure gutters and downspouts are secure, open and free of debris .
10) Check that all bathroom, kitchen and dryer vents are properly vented outside of your house and not terminating in the attic