Floor plan design single-family house approx. 230 sqm plus basement

Ok. Then just say that it can also be 900,000 € for the house because you have the buffer. Otherwise, no discussion makes sense if the project is already dead before the building application is submitted.

Yes, the construction costs are important. In this thread, it is not about the construction costs. I want to find an optimal floor plan, preferably based on the approach I proposed. However, I am also happy to be convinced by something completely different.

Help me further where I can improve something. Where are rooms poorly / ineffectively sized? Are hallways too small / too big? Does the staircase need more space? Are children’s rooms of 16 sqm exaggerated?

I should perhaps have mentioned above:
Own contribution:
- Tiles in the basement
- Floors (except tiles in upper floor / ground floor)
- Wallpaper / interior painting work
- Garden work (100%)
- Interior doors

Yes, the construction costs are important. This thread is not about construction costs for me. I want to find an optimal floor plan.

Why should an optimal floor plan be discussed if you don’t have the money for the house? You have to consider both together, or rather, the budget actually comes before the floor plan.

So once again the question: Can you afford the house for €900,000 (+ surroundings) or not? If not, the thread can simply be closed. Because just saving a few square meters often destroys entire floor plans.

8% slope in the building envelope is not a trivial matter. That fact alone requires quite a shift in thinking (basement / cellar). And exactly as already said: floor plan and budget depend on each other. An independent consideration is not possible. There is a reason why there is a questionnaire in this forum for starters. Please fill it out, and this "Let me worry about that" somehow comes across as odd here (by which I’m politely saying that you might be driving away potential helpers).

It's less about whether I can afford it or not. For me, it's about the planning

I have been here long enough to confidently tell you that for a large majority of at least the regular helpful discussants it is significantly relevant whether a construction project or a hopeless pipe dream is up for discussion. Where someone still needs a little push or encouragement, people are happy to help. But nobody is left to ruin here. This is not a bug, but a feature ;-)

Furthermore, I have to disagree with you: It does not have to be both above the assessment limit.

Mea culpa. I meant, of course: "... provided you like to sleep calmly and do not need the thrill of existential fears." I myself live in the jurisdiction of a very nice bailiff – nevertheless, I prefer it when she rings elsewhere. Professionally, I only advise builders, but voluntarily also debtors. That sharpens the view for tightrope walkers ;-)

Help me further where I can improve something. Where are rooms poorly/not efficiently sized? Are hallways too small/too big? Does the staircase need more space? Are 16 sqm children's rooms exaggerated?

If you looked at your design with planning experience, you would notice it immediately. But a staircase inserted only as a symbol is even difficult for to assess ;-)

Why should an optimal floor plan be discussed if you don't have the money for the house? You have to consider both together, or rather the budget even comes before the floor plan.

So once again the question: Can you afford the house for €900,000 (+ surroundings) or not? If not, the thread can simply be closed. Because just saving a few square meters often destroys entire floor plans.

Yes. You will throw out a number without exactly describing how you came to it. Please explain how you arrived at this value?