Cost planning for construction financing - how specific does it need to be?

Converting the house is not an option! You just have to come to terms with the fact that the house has to be torn down. I am willing to pay the price. The price is not the problem.

To quote an architect: There is no new construction on Köln soil under 1 million including the land ... With your 450,000 for a house you will certainly find something, but you should be clear that it will neither be an architectural icon, nor will you be able to install unimaginable luxury. The remaining 200,000 quickly go for the architect and other incidental construction costs, garages, outdoor facilities and garden design, enclosure as you mentioned (wall?), residential ventilation, indoor/outdoor lighting, possibly special requests such as room height doors, aluminum windows, a kitchen is quickly five digits with the first digit >5, i.e. this is no longer uncommon today in these properties.

One more question about your calculation: You have taken into account the property transfer tax (6.5%), broker (3.57%), and notary (1-2%) in your calculation, as well as demolition costs (>30 TEUR). Then I come to about 740 TEUR for the plot of land, provided you can take over the old development ([Kanal aus den 60ern???]).

The plot costs 550 TEUR. In addition, 9% incidental costs 50 TEUR and broker 20 TEUR = 620 TEUR for the plot.

Whereas the question is what additional development costs will come..... the city of Frechen cannot answer this according to the letter.

For the demolition, planning, the house, and the rest, there remained about 680,000 TEUR.