Baunebenkosten calculation realistic?

Basically, I totally agree with you. However, if I have the choice between no house or a house with concrete blocks, the choice is clear. So your argument isn't really an argument. Above all, this can be extended arbitrarily. Personally, I prefer to see my whirlpool every day when I go into the bathroom. If you don't care whether you can relax or not, then that's fine.

Yeah, and what is this information supposed to do for me now??

If it's just a few thousand euros missing and the budget was so tight, one should generally consider whether they can afford to build.

So if you have, for example, many trees in the area, you will see the difference after 5 years at the latest. Your roof will look as if it were 20 years old. Simply running Kircher over it is not so easy on concrete. The risk of damage is higher there.

The problem with your way of thinking is precisely that it usually does not only apply to the roof tiles but consistently runs through everything: three dozen extra sockets here, a masonry double garage instead of carports there, marble tiles instead of porcelain stoneware, and so on. And then the question posed by Joedreck arises... accept that everyone has their own budget and is allowed to spend it on what they personally consider important.