Solar in Philadelphia is a small rowhouse roof, usually low-slope, hemmed in by parapets and the next cornice. Shade arrives early from the houses beside you and from a tree in a yard the size of a room. The covering may be a patched membrane that already ponds. That pond is the first subject. Racks do not go down on a roof that holds water or on a deck you have not seen. If you do not control the roof alone, say who does. Many rows are simple houses. Some are not.
The layout has to leave the drains, the party-wall flashing, and a way to the hatch. A deck, a condenser, or a skylight may already own the sunny part. Attachments and flashing have to suit a flat covering, not a shingle slope copied from a hill house. Wind still gets at a roof even on a flat street. The electrical service is often an older basement panel at the end of a narrow stair. Do not guess its condition. Say whether you have looked at it, and whether the house has one meter.
Say which direction is open to the sky and what cuts it off after midday. A satellite square will miss a soft spot and a scupper. If the top floor already stains after rain, the roof work is ahead of any array. Ask who pulls the permit and who files the interconnection. Ask how penetrations are flashed and what happens to the modules when the covering is replaced. Ask who owns the equipment once it is mounted and who is called when an inverter goes quiet.
Have roof shape, leaks, shade, and access in the first minute. Access is a bulkhead and a sidewalk, not a driveway to a ridge. Leave money out of the call. Snow is a lighter part of this city's roof story than ponding and party walls, but ice at a parapet still deserves a mention if you see it. Describe the roof you walk, or the roof you are afraid to walk.
A steep clear slope is the wrong city. Solar in Philadelphia is a row roof, a parapet, and the question of whether the membrane is ready. Call the number on this page.