We are planning our house construction and are in the cost estimation phase

Good morning,
we are a family with one child and are planning to build a house.
The house is to be built on the property of the parents-in-law. However, there is still an old barn on the site. This would need to be demolished. We have already received offers for this. The demolition would cost about 20,000 EUR.
Now our question is what costs we have to expect for the house, development, and additional expenses.
We are planning a detached house built in solid construction. About 130-140 sqm and 5 rooms without a basement. The house is to have a staggered shed roof.
We have an appointment at the bank soon for financing. For this appointment, we would like to have at least a rough estimate.

Thank you very much

A rough estimate of what something like this costs is given to you by a construction company after you have told them your wishes. Your information is already quite sparse.

Very, very roughly, I would set "Schlüsselfertig" at at least €1600 per m².

Thank you very much for the response.

What additional information is still needed? I will then provide it as best as I can.
Does the 1600 EUR per sqm include additional costs? Or would the additional costs be added on top?

The typical ancillary construction costs of course still apply. What greatly influences the price are issues such as KFW55/40/40+; central controlled residential ventilation, electric shutters, the level of demand for electrics/LAN/SAT, garage/double garage, etc.

It should be a KFW 55 house. We would like an air/water heat pump for heating. Electronic roller shutters should also be installed. A LAN cable does not need to be laid in every room. The same applies to the SAT connection. Only the living room and children's room. A carport would be nice, but not absolutely necessary.

Then you will probably not manage with €1600 per m². But that's all just guesswork.

Go to 1-2 construction companies, make a very rough plan including cost estimation, add 10% on top, and you will have a rough idea of where you will end up.