Planting Terrace

It highly unlikely to be owned by the shareholder. While shareholder can go there, putting a table and chairs may interfere with the fire code especially if it is in some way connected to the fire escape path.

Actually I can see several of these in my building. In one case there is only one apartment with access (through a window to it) and in some others more than one apartment access a shared space.
There is no connection to a fire escape path.

Actually I can see several of these in my building. In one case there is only one apartment with access (through a window to it) and in some others more than one apartment access a shared space.
There is no connection to a fire escape path.

Actually I can see several of these in my building. In one case there is only one apartment with access (through a window to it) and in some others more than one apartment access a shared space.
There is no connection to a fire escape path.

Unless someone is Spider-Man and can swing down 30+ stories to the street

Highly unlikely that the shareholder would have any 'ownership' of that terrace space (more technically correct: the shareholder's proprietary lease would not include any rights to use that space). If there's no evidence that the space was ever correctly developed as a usable space (i.e., a real door for access, proper decking over the roof structure), it's the co-op's, not the shareholder's.

I would be very cautious about units adjacent to such setbacks that don't include some part of the space in the proprietary lease -- I remember a thread somewhere on SE about a court case where the co-op put commercial AC units on the setback roof (to cool the commercial tenant below), which were more or less right outside a shareholder's unit. Much drama ensued.