Dark, "dirty-looking" areas on your roof.
Possible causes: Environmental pollutants; vegitation, fungus or algae growth; loss of granules due to age of shingle

Missing, cracked or curling shingles.
Possible cause: Shingles have reached their useful life.

Leakage in attic after driving rain.
Possible causes: Leaky or inadequate shingle underlayment; deteriorated flashing.

Roof shingle, sheathing, and siding decay.
Possible cause: Poor attic ventilation.

Blistering and/or peeling of outside paint.
Possible cause: Excessive moisture or high humidity due to poor attic ventilation.

Stains on interior ceilings and walls.
Possible cause: Inadequate or faulty shingle underlayment allowing leakage from ice dams.

Excessive energy costs.
Possible cause: Insufficient attic ventilation causes heating/cooling system to run excessively.