Semi-detached house in Hamburg with general contractor on own land (two + full attic floor, no basement)

Maybe a general contractor who works according to his approach would prefer to do his own (re)planning, which would then cost me money again, so that I partly pay twice and end up stuck with the additional costs. Or where am I thinking wrong?

Yes. If you tell him that you want the planned house, then you will get it. The general contractor is just an agent who does what you want. He who pays the piper calls the tune. And if you want 17 rooms of 8sqm each in the house (and the architect has planned it that way), then he will build you that house. The general contractor couldn’t care less how crazy or outstanding your house becomes. He just builds it.

Maybe like this (all sqm values just rough estimates):
Ground floor: living-dining area with kitchen (30 sqm), technical room (8 sqm), guest bathroom (one party with shower) (5 sqm), rest (14 sqm) divided between hallway and another room (guest/work).

30 sqm for 5 people is already quite a challenge.
I’m not a fan of sticking to fixed sqm sizes - a poorly planned 15 sqm room can have less usable space than a 10 or 12 sqm room. But a dining table of course also needs space around it to sit, a family sofa should be larger than an KLIPPAN from Ikea. And a kitchen needs adequate cabinets as well as a worktop.
However, you forget the stairs. 8 sqm technical room for a KfW40+ standard can be enough, but you probably also want to accommodate laundry washing and a broom.

also proper heating etc.

Without it, it wouldn’t be a living space.

Declaration of battle

Actually, I wanted to deliberately talk about general things first. Now there are numbers (and the estimate is just to show that we have thought about square meters per floor). With what you, , write, a room would definitely have to move to a higher floor. But then the attic would be needed as living space. And the thread is partly about exactly this question, whether and how we need / can afford / can structurally design the attic. And about what tips you have on how we should think further.

Regarding other things (e.g. kfw40+ & financing framework), I have already written something above; I am waiting for comments first.

Yes. If you tell him that you want the planned house, then you will get it. The general contractor is just an agent who does what you want. He who pays calls the tune.

Interesting. Do Baudirekt and Viebrockhaus, etc., see themselves as such agents? I would guess that Viebrockhaus, for example, only builds its own houses. Or are they not general contractors and I have mixed up some terms here?

Interesting. Do they understand each other … etc. as such agents? I would assume that Viebrockhaus, for example, only builds its own houses. Or are they not a general contractor and I have confused the terms here?

These are primarily providers of their own houses. The classic general contractor is a construction company or a carpentry business. Often local providers.

Viebrockhaus & Co.: furniture store
GU: local carpenter

For understanding

The classic general contractor is a construction company or a carpentry business. Preferably local providers. [...] For understanding

Thank you! Then there would also be a question whether we should go with such a general contractor or with a provider of their own houses with our ideas. Maybe something can be achieved through adjustments that is cheaper and somewhat meets our ideas. (Viebrockhaus would probably not be an option for us - btw.)