Whenever possible I will get up on to the roof to perform a walk on inspection. Not all roofs lend themselves to a walk on inspection. Things like roof height, steep pitch, roofing materials and snow cover can prevent a walk on inspection. In those cases, I have a telescopic pole with a high definition camera system that allows me to take images of the roof when I cannot get up on it. In either case, whether seeing firsthand on inspecting photos, the things I look for are:
The type and condition of roofing material, the conditions of roof flashings, debris or growth on the roof cover, whether penetrations (screws, nails and bolts) are visible and have been sealed, are there any missing or damaged components, and what is the approximate age of the roof.
My goal is to tell you the overall condition of the roof, whether it needs maintenance and how long you may expect it to last. The attic inspection often offers much more information on the roof cover integrity as quite often you cannot see a problem from above – water is sneaky!