Rubber flat roof on brownstone...connected to another roof

[Keely Aldinger]

I'm in the Boston area and purchased a brownstone that has one connected brownstone by a fire wall on its right side. The roof on my building is only 6yrs old and looked good during inspection. The inspector's main concern is that the connected roof does not have a drain and seemed to rely on my roof's drain and he recommended to have them sort that out.

We have had some very wet weather here and I have discovered a bit of water on the 3rd floor unit sheetrock, and some water at the wall level (same spot on the building) of the 1st floor unit resulting in some damp sheetrock.

This area of roof relates to the area of the shared drain. Google Earth shows me that water pools on the other side of this roof. Trying to figure out what the normal course of action for something like this is, since at this point we don't know the owner of the other building. (Large LLC)

I'm new, so besides getting some roofers out for estimates/assessments to see if the problem is on my side..what do I do if the problem is being caused by their side? There is no grade on their roof to guide water to my drain/gutter...just a break in the flashing that divides the two roofs. Google Earth image is from a year ago.