Yah. I too like the concept of 3-D space. But...

Thinking about what I've seen so far I doubt it. What is the meaning of "public access" here? Gated, guarded and "operated" spaces, where you need to be paying customer for some venue, or buying a ticket?

The places themselves fenced/glass walled in to discourage suicides, stupid people throwing things down from high up, even if "only" a coin?

I mean, look at anything which comes to your mind right now, where people can go high above anything else where other people are below them. It varies, but often it is heavily fenced/walled to protect the people below.

And lastly, think of "reckless youth", and how groups/gangs of them tend to ... err ... impose dominance over places they consider "theirs".

Would you want to be there?

Do tower blocks not have balconies or roof terraces where you live?

They do, but they aren't public access.

But there's no problem with kids throwing objects from the roof?

I don't recognize this gang thing, maybe because I don't live in a dense city (and don't recognize the attraction of it)

I almost never saw that, maybe because we have something like "Aufsichtspflicht" which means duty/responsibility/liability to watch and guard(over the kids). Could be different due to different demographics/ethnicities in social hot-spots now, but I don't frequent them(that much). Also the access to the roof there is closed/locked for liability reasons by the landlord. And usually the higher ones(more than 4 or 5 floors) aren't next to the street, there is some green separating them. But the residential buildings weren't really what I had in my mind when I thought about that. More like downtown, central business/commerce areas, traffic hubs, and such.