I have to say, the additional costs for the floor plan changes were very reasonable for us. In the end, we individually redesigned, moved almost every wall, etc. I believe the floor plan changes cost about 3000 euros (plans, statics) plus changed material and labor costs (all understandable and fair).
So I cannot confirm that it becomes excessively more expensive if you want it customized.
But of course, the standard does not include any luxury - many things already cost a considerable extra charge. In advance, the additional costs were also rather reluctantly disclosed... which made it a bit exhausting. However, since we ultimately did not upgrade much or only the things that were worth it to us, it was not a big problem.