Is financing a single-family house feasible for us?

Hmm, so our parents have over 200sqm of living space and are happy when someone takes care of it because it's too much for them alone. And they don't want a stranger in the house either. If our parents had to save on something, we would of course pay rent. But our parents are doing very well financially. I haven't heard of anyone rejecting their inheritance because they can manage it on their own after all. Ultimately, it is the decision of the parent generation whether they want to spend their earned money entirely themselves or pass on a part of it.

I wouldn't justify myself here if I were you. Make sure the costs stay somewhat within limits. If necessary, you can always add some financing or get support from your parents. Personally, I wouldn't do without the basement either. You'll regret it later. As civil servants, you are really in a comfortable situation. From my point of view, not much can go wrong, especially since you also seem to be frugal and likely wouldn't have any problems tightening your belt for a while.

Good luck with your project!

Hmm, so our parents have over 200 sqm of living space and are glad when someone takes care of it because it’s too much for them alone. And they don’t want a stranger in the house either. If our parents had to save on something, of course we would pay rent. But our parents are doing very well financially. I haven’t heard of anyone rejecting their inheritance because they think they can manage on their own after all. Ultimately, it is the parental generation’s decision whether they want to spend their hard-earned money completely themselves or pass on a part of it.

As well as the children whether they are so proud to manage their own life financially without parents. It always has two sides. It’s not about the inheritance at all but about living for free with the parents...

We have approximately 65 sqm of living space each on the ground floor and first floor and about 30 sqm gallery in the attic. I don’t remember the exact numbers offhand. But as already mentioned, the attic can also be postponed/left as is.

Work and guest room 30 m2? So a nice to have, for which 12 m2 in combination would easily suffice! Then there would easily be room for a craft room and the technical room in the rest. Thus, the remaining arguments for the basement are only - "party room" - "everyone has a basement anyway" (so why still build one at all!) Since civil engineering is always more expensive than above-ground construction and the huge garage will probably get a gable roof anyway: why don’t you build the craft room/storage room/workshop up there? A small spiral staircase at the back on the gable side would probably suffice.

Our neighbors, who built almost the same thing, paid 50k more. We hope, of course, that a lot of that was for the general contractor and that we still have plenty of family who can help.

When was that? 5 to 7% were typical increases in construction services in recent years. So from 500k about 3 years ago, it would also be almost 600k now.

Moving the garage, I will probably enforce that now. You can really still do that 1 year later. Better than completely ruined, broken up because of stress... And what extras are still included will probably become clear during the construction process. It was definitely interesting that many, unlike the bank, already view our construction project critically.

For example, with friends it was like this: the offer for the earthworks was 15k, but in the end the invoice was 25k.
That would break our neck

Okay, then I misunderstood that. Earthworks are a tricky thing because it really depends on the final disposal costs. It can be 8k but also 20k. That is the disadvantage with a basement. The garden work and marking out can be calculated better. With such differences there must also be a supplementary offer and then you can still decide.