rooftop addition in landmark district

I have the right to add a rooftop addition to a 5 story corner tenement building in New York City. The building is in a C2-7A zone (residential equivalent of R9A) so we should be OK on FAR, but the building is within the Upper West Side Historic District. I own the existing apartment under 2/3 of the roof. I expect we will need to set back, and hopefully we can get 1200SF of new building on the existing 2200SF building. Style is flexible, but if setback gives us design freedom, prefer a modern glass design to connect with the rooftop garden in the setback area. Looking for an architect with experience in rooftop additions and NYC Landmarks, or a brilliant creative who feels that they can navigate this thicket. Thanks !