In short: My recommendation would be to discuss your ideas with the person responsible for you at the building authority. That costs nothing and at least gives you a rough idea of whether your ideas are feasible.
I have done that (see above the italicized text; those are the building authority’s responses). They only conduct a building consultation if an architect’s draft is available. Until then, I have to live with the statements made so far.
Look at the neighboring buildings: what you see there will definitely be possible.
I think we’re beyond that point when reading the contact with the building authority. In the area, there are almost exclusively bungalows or 1.5-story houses. However, there are also a few newer houses in the neighborhood with 2 full stories and flat roofs. And the building authority signals in the email that this would probably be possible as long as an open construction method is followed...
Otherwise, the topic would be settled for us. We have defined the feasibility of 2 full stories as a dealbreaker...
I just find it a pity that you can’t get into a conversation with the building authority without first having an architect’s draft. If I had only listened to the general contractor – “You will never get approval for 2 full stories there.” – then I wouldn’t even have bothered with the topic. But as I said, the building authority expresses itself differently in the email. The problem is, that is not legally binding and I trust a few lines in an email less than if you sit down for 20 minutes, calmly talk about the property, and then they give a clear oral signal that we can plan with two full stories and that maybe there will be some adjustments here or there if necessary...
After all, I have to buy the property before I have an approved building permit here... or you would have to commission the general contractor to prepare a comprehensive architect’s draft without knowing whether a notary appointment will even take place, etc.
I have sent the building authority the rough draft of the 200m² model house with 2 full stories and am still waiting for feedback on that at the beginning of January.