Roofing in Pennsylvania splits as soon as you look up. Many Philadelphia rows carry a low-slope or flat roof behind a parapet, and the leak is a pond, a seam, or a party-wall flashing. Pittsburgh houses on hills usually carry a pitch, often a steep one, and the leak is an eave, a valley, ice, or a chimney. Philadelphia rowhouses are not Pittsburgh houses on hills. Detached houses elsewhere are mostly pitched too, with ice and wind of their own. Say the shape before the stain.
Timing tells the jobs apart. A flat row roof drips during rain and after it, while water sits. A steep hill roof drips when snow melts and ice has choked the eave, or when wind drives rain under a lifted tab. Granules in a downspout, a cornice that is itself the leak, and daylight in an attic are different clues. The northwest can add a heavier snow load than a southern row ever sees. Do not walk a steep icy slope or a soft flat roof to get a better look.
Neighbors change the work on a row. Their roof may drain onto yours, and the flashing you need may sit on a wall you share. On a hill, the lower roof catches what slides off the upper one, and a gutter full of ice can rip loose. Say if the covering has been coated, layered, or patched. Say if a deck or a rack is already fastened through it. Access on a row is a bulkhead and a street. Access on a hill may be steps. Mention which.
Say leak, age, or storm. Ask about the deck, the way water is supposed to leave, and flashing at walls. Ice-dam leaks are not solved by a patch in the middle of the field. Ponding is not solved by a shingle detail. If you need a dry-in while the season continues, say so. If the attic is warm enough to melt snow from below, say that too. It is part of the roof story.
Pick the roof you have, not the roof in the other city. Roofing in Pennsylvania is a parapet pond or a steep eave, and pretending otherwise repeats the leak. Call the number on this page.