It is important to us that we already have the rough floor plan so that we can also calculate a price.
Not to the providers. They need the living area, not the floor plan. They don't care where the walls are located. By the way, I have a déjà-vu with that floor plan (with the one from Ev-Marie86).
In our floor plan, we have the exterior dimensions of 9.63 x 9.82.5, I have subtracted all walls from this floor plan and added them to the living area, so it should correspond to 130 m2. Is that correct? It seems a bit large to me.
Methodically, a faulty calculation result is absolutely to be expected here.
Now the question arises how large the house actually is. One home builder company talks about usable area, another about living area or built-up area.
What the house stands on on the plot is the built-up area (footprint). Walls are subtracted from that. Remaining are living areas, usable areas, and traffic areas. You can google all the relevant standards yourself.
In practice, rough rules of thumb will suffice. The term one-and-a-half stories can be taken quite literally. A target size of 130 sqm would thus be divided by 1.5 per floor, approximately 87 sqm. Similarly roughly, you can calculate about five quarters for wall area deduction. Ultimately, this translates to just under 110 sqm footprint.
9.63 x 9.825 m (I won’t even ask how that came about) are, according to Eva Zwerg, significantly less. Built on this footprint, a two-story house would be about 150 sqm – but a one-and-a-half-story house rather just over 110 sqm.
But that’s only as a content-related answer to the factual question; regarding the qualitative assessment of the "floor plan" – both in planning terms and as a basis for price inquiries – I fully agree with my predecessors.