So I knew right from the start that most people wouldn't take it seriously ;p
As I said, the 20k are pure material costs without architect, structural engineer, and mandatory connections.
Otherwise, of course, we would also take B-stock, used, etc., if available in reasonable quality. From an ecological point of view even sensible, since not everything has to be new.
I have already researched costs for windows, doors, etc. What I still find difficult are the ceilings (basement, intermediate ceiling possibly, and roof). Is it even possible to do that yourself?
Which energy saving regulations and DIN standards would be particularly important for a building permit?