I also really like the book stairs, but my husband wished for them. I don't really care which wood, as long as it's wood. I think I heard that a concrete staircase is cheaper. But I don't want to commit to that.
However, I had never had a wooden staircase before and was a bit afraid that it would creak. The staircase builder then sold me one where the steps sit on rubber anchors in the wall. He said it would only be slightly more expensive. Our general contractor later doubted that in front of me, but did not charge me extra for it.
Thanks for your contribution. I first had to look up "Flachdacherker" online, that really is a great gain in space. And you actually preferred a concrete staircase to a wooden one? Why is that? Oh, the furniture isn't meant to last forever...
But I think that only works with open stairs without risers. However, I assume you have one like that. Because you wanted the wooden staircase for aesthetic reasons, and such an open staircase appears even lighter and brighter..?