Solar in Pennsylvania has two roofs and they do not pretend to be one. A Philadelphia row is often a small low-slope surface behind a parapet, shaded by the next cornice and shared in spirit with the party wall. A Pittsburgh house follows the hill, so the slopes face whatever the street did, not the sun you wish you had. Philadelphia rowhouses are not Pittsburgh houses on hills. Snow and ice still visit both, heavier on the steeper western roofs. If the covering is tired, roof work comes before any rack.
Shade and structure are the site. On a row, the next house, a parapet, and a tree in a tiny yard cut the useful area. On a hill, trees above the house and a steep pitch change how snow slides and how rails attach. Say which way the surfaces face and what shades them after lunch. The electrical service in an older row or hill house may be crowded. Do not guess a size you have not read.
Flashing has to match the covering you have, membrane or shingles, and it has to live with ice at an eave or with water that sits on a flat roof. Ask what happens to the array when that covering is replaced. Ask who pulls the permit and who files the interconnection. Ask who owns the modules once they are up and who is called when an inverter goes quiet. If you do not control the roof, say so. A row roof can be a building question. A hill roof is usually the house, and the walk to it may be steps.
Have the shape, the condition, and the shade in the first minute. Mention ice dams if they are already a habit, or ponding if the roof holds water after rain. A picture from above has not seen a soft deck, a party-wall flashing, or an attic full of frost. Leave money out of the call. The site is the whole subject: flat row, steep hill, or a detached roof that is neither.
Panels do not flatten a hill or dry a ponding roof. Solar in Pennsylvania is the surface you actually have and the winter that sits on it. Call the number on this page.