Using binoculars, a pole or drone to inspect your roof should be a last resort. Its always better, and in many cases, faster to walk the roof. When walking the roof, not only are the shingles observed in hidden spots, but any deflection can be felt or seen. Deflection may be from rotted sheathing or under designed rafters. Many older homes (1950’s) have under sized rafters causing the roof to sag 2 or 3 inches. This may be due to missing collar ties, poor bracing or location of bracing in the attic. This may be a simple fix that your contractor can take care of by following the latest building code. In other cases, engineer involvement is advised. Again, if safe to do so, the roof should always be walked by your home inspector to ensure a proper quality inspection.