I would be concerned about the drainage. Having water sit for a day or two is generally not a good thing. I think raised beds (I'm thinking like raised beds that are tables) might be your best bet

Here is a link that might be useful: Raised bed tables

Container gardening is the way I would go. You can have a lush looking patio now, and take the plants with you, or sell them if you move.

I agree that container gardening is the way to go. I also live in Philadelphia. I grow my vegetables in containers in my yard. I went to Home Depot and bought 6 concrete blocks and a piece of ply wood. I put my containers on top. The raised bed planters are also very nice that were recommended.

Amsonia that is a lovely garden.

You just gave me an idea to do the same maybe next year but I would face problems, one being that the Super here even if I got permission to garden in the enclosed courtyard would sabotage my garden along with some of the tenants.

There used to be about two or three strips of exposed dirt like what you see in the center of parked cars to keep them parking straight. I eyed those dreaming about one day planting a garden but the Super is such a tool I never inquired. Well eventually the LL covered them over with concrete. :(

I heard the Super is leaving (God I hope this is true) so I might work up the nerve for a roof garden. Or I might try a vertical garden and pray no one bothers it.