Looking for a single-family house with a 8.5m-wide eaves side

Well, then talk to those, they are definitely cheaper than Viebrockhaus and you will also get a proper house.

With Viebrockhaus, we unfortunately pay €25,000 just for the roof rotation (gable end roof is not standard).

They charge well for such changes.
When the roof is rotated, the gable also becomes larger and the roof higher, which causes such costs.

Is Viebrockhaus actually that ridiculously expensive or should we expect similar prices from other providers?

Yeah, they are more expensive than others...

There are plenty of providers who will build it for you more cost-neutrally.
Possibly regional providers who don’t just pick from standard house models but pay architects to design something nice that meets the requirements.

If I don't have a standard plot, then no standard prefab design fits on it either! Either find providers who plan more individually or go straight to an architect.

Have a look at Fingerhut Haus single-family house Berlin

I would talk to a few companies. Show home park, regional companies
Maybe you can also adapt a standard semi-detached house

I agree with that: the "Dachdreherei" (roof twisting) with a detached catalog house is, in my opinion, the unnecessarily convoluted way – I would rather look at semi-detached house models. In this format, it should be easy to find something suitable. From my point of view, this task almost screams to build a detached semi-detached house, where the window on the fourth side will not be harmed.

You were probably at the Viebrockhaus model homes in Kaarst. These are adapted to the local price level. I know a home builder who has already reliably, fairly, and affordably built with stone as a general contractor at a fixed price for friends and their daughter in the Viersen district. Please send me a private message if necessary, and I will gladly establish contact. I am sure you can take a look at one of the houses in Niederkrüchten.