Architect's house in Pforzheim - Offer too expensive?

By now too precise, unfortunately.
But there are already some pretty ugly buildings in places, as quoted above.

Well, I don’t know every house but do you have an example?

The next time I go for a walk there, I will take a few photos

A very rough estimate states that the construction of the basement for an ordinary single-family house costs around €50,000. By the way, that's as much as a solid double garage completely built by companies (brick by brick, concrete foundation, windows, roof, plaster, electric gate).

I think building the 3rd floor and finishing the roof structure will hardly be cheaper. Additionally, the development plan must allow the height of the house (which is probably the case with the OP). Also not to be underestimated are possibly necessary gables, windows, shutters, drywall, etc., which are needed for a habitable attic.

I know many who have skipped the basement for cost reasons. The consequence: all the junk that would actually be stored there is then kept in the garden or the garage, and the car is parked outside.

All in all, a basement level is probably cheaper and less complex. And if you think, for example, 10 years ahead: expanding a house upwards by one floor is expensive but somehow feasible. Building a basement under an existing house is more difficult.

A very rough estimate states that constructing the basement of a typical single-family house costs around €50,000. By the way, that's about the same as a solid double garage completely built by companies (brick by brick, concrete foundation, windows, roof, plaster, electric gate).

I think building the third floor and converting the attic will hardly be cheaper. Additionally, the development plan must allow the height of the house (which is probably the case with the OP). Also not to be underestimated are possibly necessary gables, windows, roller shutters, drywall, etc., which are needed for a habitable attic.

I know many who have foregone the basement for cost reasons. The consequence: all the junk that would normally be stored there ends up in the garden or garage, and the car is parked outside.

All in all, a basement level is probably cheaper and less complicated. And thinking 10 years ahead: expanding a house by one floor upwards is expensive but somehow doable. Building a basement under an existing house is more difficult.

The calculation does not add up. Today no one builds a basement (white tank and everything a bit properly done) for 50k.

A habitable attic is significantly cheaper. For us, it was almost exactly €15,000 (and we certainly didn't build cheaply) to turn a cold roof into a warm roof (including higher knee wall, heating, insulation, drywall, plaster, windows, flooring).

PS: and I am PRO basement!!! If I were to start again today... I would build WITH a basement and attic

The house has a flat roof
Permissible height would fit with a 3-story construction.