I recently built a roof over my portch and now the entrance cable goes through it. The weatherhead is still a good 18" above the new roof but a friend said I may want to put up a new mast service for safety. What should I do before calling an inspector in?

Tough call.

Sounds like you built a porch roof up to and attached to the main building, and around the SE cable that is strapped to the exterior of the main building.

I would call the inspector in and get his ruling.

If the structure has a ceiling, creating a closed in attic, so to speak, I would say the SE cable is now inside the building, and require conduit.

If there is no ceiling, and the underside of the roof can be seen, then I would say the cable is outside the building, and allow it as is, as long as the cable is protected from the roofing/structure material.