Very rough single-family house price estimate

What a wonderful answer.

Of course, the decision for/against an (additional) child is not made by the house.

But for example whether there will be a hobby room and a guest room, that is decided. And whether the children's rooms can be more spacious, for example, and so on.

No one said that I will build bigger if I can. But maybe I would have to build smaller than I would like. And knowing that can't hurt.

But maybe I would have to build smaller than I would like. And knowing that can't hurt

Theoretically yes – in practice the "conclusion" is unfortunately naive and a misconception, that one could divide their budget by a locally usual price per square meter or cubic meter for a category X of demand and then get as a result the house size they could afford. You will not be able to aim at a floor plan selection within plus or minus 10 sqm. Rather, on the contrary, you will probably have to "spend" part of your budget precisely on not being able to deduct a portion of area or features from a house plan not to make it fit the budget.

Calculate with 1800 to 2000 euros per square meter without additional construction costs and without land

What 11ant wants to say is you first need a room program with approximate sizes and then you have to see if it fits into your budget. Yes, a children's room can be 12 or 20 sqm. But 3 children's rooms, 1 study, 1 hobby room for the model railway, 1 dressing room with an 8-meter closet for the handbag collection cannot be shrunk together to 130 sqm.

Which rooms do you need
How big should they be
(Sample houses give a feeling for this)

How do the numbers look? Have you defined a budget and financing framework for yourselves where you can live well? Guide us through the numbers