There are always three main problems with roof decks in the city if you accept municipal permission as a given.
1. How do you get the materials up to above three stories.
2. How do you secure the deck to the top of the building where wind loads are their most ferocious.
3. How do you get the humans up to enjoy their deck.

Answers:
1. Boom truck with a skilled loader.
2. Bolting through to the masonry walls with anchoring cement or epoxy.
3. Stairs.

After that it’s just some skill and heavy lifting. In this instance, at the south end of the deck the roof was built on top of the walls rather than engaged in the wall. We cut down through the roof and built up C.M.U. piers from the masonry bearing walls, anchoring down into the wall 6 or 8 courses with rebar up through the piers to brackets attached to the post bottoms. Then the whole assembly had to be reintegrated with the roofing system and we capped the pier with heavy metal flashing like a little roof on top of it to guarantee no water getting behind the roofing material.

We took advantage of an existing window to cut in a door with attention to floor elevation vrs. roof and deck elevation. See more photos here.