Things to look at from the inside:
1. Dark spots and trails
2. Signs of water damage or leaking
3. Places where roof deck is sagging
Things to look at from the outside;
4. Inspect your roof for cracked, torn or missing shingles
5. Look for loose material or wear around chimeys, vents, pipes or other penetrations
6. Excessive amount of shingle granules in gutters (this is sign of advanced wear)
7. Check for signs of moisture, rot or mold (mold, fungi and bacteria can grow quickly)
8. Check drainage and make sure gutters and downspouts are securely attached. Also make sure all drains are open and allow water to exit and that gutters and downspouts are free of debris