If 2000.00 € remain - build a house or not?

Since I come from the finance sector, I can actually only confirm the 500 euros per 100,000 loan. This is always a quite good first point of reference for what is possible and what is not. Of course, in a low-interest environment, it can always look different, but a residential construction financing is long-term and anyone who thinks back 20 years also knows what interest rate levels prevailed back then. Something like that can happen to us again at any time - in the long run.

I once made a household budget and came to the conclusion that with all expenses (car, insurance, "luxury", eating out, cinema, trips, clothes, etc. etc.) we have about €2000 net available per month.

€1000 in expenses? What about vacations, reserves for other investments (repairs, furniture, new car, etc.), ... Are no children planned? What about unemployment or if something happens to you? So I would rather assume double the amount, otherwise you are very frugal. In my opinion, the amount is too tight. Furthermore, you say on the one hand you currently save €2000 per month, but with the apartment you could not save €60,000 equity in 5 years. That somehow does not add up.

(€2000 - €1000 housing costs etc.)*12*5 = €60,000