yes, that's how it should be We need to gain more space upstairs.
You "might have to" gain space, but not in this house.
and does it even work?
Generally, yes and no, economically even never ever. The extension costs (excluding garage and excluding dismantling, storage, and reassembly of the existing roof structure - I already mentioned that it only partially covers the "staircase") - about as much in euros as the entire house cost back then in marks.
My parents don't want to enlarge - maybe they would be willing to enlarge the kitchen.
But they are willing to accept the shading that a protruding attic like prostitute's claws will bring to their living floor, and to make their beautiful house virtually available to you as an above-ground partially basemented penthouse with a larger footprint? - then I hope you are an only child; as a co-inheriting sibling, I would question their full mental capacity at that point.
It's not that simple, since you have to observe boundaries and, as you say, the building is very angled. I would like a bigger living room and kitchen, and I think you would have to extend even further out. Part of the annex would be built using timber construction.
I said nothing about angled. The house, as it stands, has a charm that, while not to my taste, certainly has its market niche. With the addition of a Frankenstein treehouse, you’re ruining that; then even Horst from "Bares für Rares" wouldn’t like it anymore. Your "concept," to place an attic separately to the boundaries of the building window, is hopefully — aesthetics being one criterion, adherence to the building window not being the only framework — not approvable; the principle "perversity costs extra" would surely evaluate that in textbook fashion. The wishful thinking that executing the cantilevered parts in timber construction could save the nonsense structurally will not work.