Attic training at a flat roof

Without parapet, it won't work. The concrete slab will still have the appropriate (slope) insulation on it.

What does "heftig teuer" mean?

The parapet can also be made of reinforced concrete, practically poured together with the concrete slab.

When the ceiling is being poured, what speaks against letting a few anchors stick out and using them as stability for the [Attika].

But what price are we talking about here?

What also sounds strange, a bitumen membrane? Think about it carefully, better go with EPDM, it holds better and lasts longer.

How high was the offer then?

EPDM ... try to find someone who installs it in that size and with the necessary penetrations. And then it costs many thousands in additional charges. In my opinion, there is nothing to object to against the usual three-layer structure.

I would also be interested in what the parapet should cost.

For the parapet with a row of Poroton bricks and a concreted U-shell, I was at about 100 euros per meter. I find that already expensive. The parapet cannot be concreted at the same time. First, the ceiling would have to be poured, and then the upstand could be shuttered and concreted. The solution with the calcium silicate bricks still sounds inexpensive and easy to build to me.