Single-family house of 200m² in 45° angled construction

But I find the design bold and refreshing.

I agree. And as so often, these designs are not cost-optimized. When a plan is priced, it is usual that those asked only price what they see and leave out what they don’t see. The first bearer of "bad news" (it will be more expensive) is, by experience, too often out of the running for the contract. From this mechanism and an idea of current construction prices, I also think that the costs will be significantly six-figure above the sums currently being discussed. So what – if it remains affordable for the builders? I know people who have gone far six-figure beyond the first calculations and do not regret it at all.

The polygonal areas on the ground floor and first floor are interesting and can be used sensibly or simply create room to breathe – downstairs a dining area can extend into this area, upstairs a nice communal play area for the children is created.

90° angles or not – the builders have to like it, the neighbors should not be too upset, because a hostile neighborhood is poison for a good quality of life. I think the slight kink fits well with the property.

What I would still think further about is:

[*
the stair area, which seems too narrow to me in relation to the otherwise spaciousness of the house
[*]the expected "quietness" in the study – how compatible is this in practice with children and garden in summer?
[*]building age-appropriately or not – the former would have a few more consequences
[*]does a bedroom work facing the "noisy" street?
[*]How do we live with
[LIST]
[*]toddlers
[*]teenagers
[*]adult nest stayers
[*]working from home
[*]socializing and guests

So what - as long as it remains affordable for the builders?

Yes if. I see an 8 right at the front here, what do you think?

No idea, it also depends on the wishes regarding the construction type, the interior fittings, the surfaces ... It can easily start with a 1 if you don't hold back. A 5 in front requires a lot of discipline, luck, and prioritization, postponing trades to "later" and/or doing the work yourself. An 8 in front is by no means out of the question.

Experience, darling...

KFW40+ house -> expect at least €2,200 per sqm.

Of course, they'll initially give you a nice estimate, they want the contract after all...

a 7 will be placed in front. Of course, everything above is open. Below only with a lot of own effort or shift and accept that, for example, the electrical wiring in the basement is plastered over.

Is the disposal for the excavation listed anywhere

I find the floor plan interesting. However, the master bedroom certainly has more potential. Bed to the right, door to the left .... try out some variations