All Roofs Can Leak!
A home inspector must inspect the roof because any roof can leak, and it's required by the standards of practice.
To inspect a roof that is inaccessible or that can not be walked on safely, the inspector may use binoculars, look from other vantage points, use a drone, use an extendable non-conductive pole with a camera, or use a ladder to get to the roof’s edge.
If a home inspector can not see the roof covering, it's a good idea to disclaim that system in the inspection report. Describe it in the report as something that was not inspected and should be looked at by someone who can reach the roof surface.
As a home inspector, you should inspect the roof covering and look for deteriorating or loosening of flashing, signs of damage to the roof covering material, and for debris that can clog valleys and gutters. Carefully look at the home’s exterior walls and trim for deterioration developing beneath the eaves of sloped roofs, especially when there are no overhangs or gutters.
Roofs are designed to be water-resistant. Roofs are not designed to be waterproof. Eventually, the roof system will leak. No one can predict when, where, or how a roof will leak.
The home inspector should describe the type of roof-covering materials in the inspection report. And the inspector should report as in need of correction any observed indications of active roof leaks.