Flat roof waterproofing terrace / flooring

Thank you very much for the answers. Unfortunately, the sloped insulation with a 2-degree incline is rather off the table. Do you have any ideas for a covering? We have already thought about a 1-degree slope in the screed so that we would at least have some slope and then put a relatively thin structure on top. The covering would then have 7cm - 4.3cm -> 2.7cm left. The cistern is a good idea, thanks!

However, sloped insulation would be preferable in terms of build-up thickness than doing it with screed. Or do you actually not need any insulation? Then screed is naturally preferable, at least from a price perspective.

And to repeat once more, if you really have 7m of slope away from the door at 2%, there is zero room for a floor covering. But you could also do a counter-slope, so that the water is directed to a drain in the middle of the roof (impact on the room below), or leads to a channel that then drains to a drainage point.

0% slope is also sufficient, as your architect already says. However, the roof must be constructed accordingly. You don’t need to negotiate this; no one will make this decision for you. It is your risk as the builder.

Yes, you are probably right. I am merely looking for alternatives and wondering how other builders have solved such a problem.

And what if you do without the threshold-free balcony door? Besides rain, there is also snow.

Honestly, rather reluctantly, but that's probably how it will turn out.