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If you can provide him with a "95% certain" floor plan as a calculation basis, I don't understand why you should still pay amount X as a planning/calculation basis.

If you can provide him with a "95% certain" floor plan as a basis for calculation, I don't understand why you should still pay amount X as a planning/calculation basis.

For the transfer of the sketch into a buildable plan, he says and calls that "preliminary planning".

We are allowed to build as if the areas in the development plan were buildable due to the exemptions. (The areas may be compensated elsewhere.) We comply with the requirements of the development plan.

That means, while adhering to the floor area ratio, you want to "relocate" the building envelope? – and under this condition, the building authority already agrees to the exemption in advance??

It’s really just about sketches. I haven’t planned anything exact, but I’m trying to roughly hit the wall thicknesses

In the preliminary draft stage – and especially in the brainstorming phase – an exterior wall is forty centimeters thick and interior walls (to which a load-bearing role is assumed here at first) are twenty, (period, an ex-chancellor would have added). You don’t have to worry about Pentecost Tuesday in leap years yet.

If you can provide him with a "95% certain" floor plan as a basis for calculation, I don't understand why you should still pay amount X as a planning/calculation basis.

Because a) a sketch is not a reasonable basis for planning and b) a floor plan in itself says nothing about the price of the house. The house does not only consist of a few bricks. The question is which insulation level with which materials, which interior finishing (floors, bathrooms, walls, etc.), which electrical system, which heating, and so on. You also don't go to the car dealership and say, I want a car like a Golf. But which equipment, you don't say.

Because a) a sketch is not a reasonable basis for planning and b) a floor plan by itself does not say anything about the price of the house.

Correct. However, a floor plan multiplied by the provider's standard construction service description already provides a basis for them to name a round of 16 price (for the decision "knocked out or continue negotiating"); furthermore, they can already check whether they have one or two similar models in the drawer on which they could build.

The house does not consist of just a few stones.

Ahoy there, Captain Obvious!
Please spare me such smart-alecky and not very funny pseudo-explanations that nobody needs.

Because a) a sketch is not a reasonable basis for planning and b) a floor plan by itself says nothing about the price of the house.

Regarding a) Yes, it is. For us, it went exactly like that.
Regarding b) I neither said nor implied that. I’ll gladly explain it to you anyway: The offer includes a construction service description for this purpose.