I am thinking of adding a really nice rooftop terrace area to a luxury rental building in SoHo. The area would be roughly 5,000 sq ft. It would be expensive to do but I think add a lot of value for each apt holder.

As an amenity how much value does a nice rooftop add to the building in term of rent per tenant? Is it worth an extra $50/unit/month? I have no idea how to price this and although I wish to do it, I need to figure out how much value it adds to each unit.