Oh yes, one more question about the picture: Can you go out into the open (like a kind of terrace) from the protrusion on the ground floor to the upper floor, or is it just visually extended without direct use above?
Then the cost/benefit factor is not really given – you could have simply made the upper floor a bit bigger and saved on sealing etc. (+ possibly problems with leaks at some point?)
Or is it no longer that expensive or comparable to the problems of earlier flat roofs?