Prefabricated house and land calculated - under €600,000?

Off topic!

Well, I can imagine nicer things, which is why my house is only 112sqm. In my opinion, children don’t need that much luxury; if you want peace and quiet, you can go for a walk or visit a friend. I certainly won’t build a castle with X rooms.

To each their own. Living is as individual for people as the conditions for financing.
People are individual, as are their needs.
It may be that 112sqm is enough for you and you find anything bigger unpleasant. It may also be that you forego something others take for granted, e.g., privacy in a family unit and corresponding home.
And yes, you can go outside, be sent to the cinema, make arrangements, etc.
But you can also enjoy building according to current needs and later use the space for yourself or for the grandchildren.
You can also be generous when others can and want to afford it.
Your post is somewhat dismissive, which really isn’t necessary.

This text has nothing to do with the quotes. Instead of rambling on about anything, you can also just admit if you confused something. We're not machines here.

Which text, which quotes, which non-machines confuse what? - I can't even remotely follow. Has your post been misplaced in the thread (/ where did it belong)?

A super flexible family cave, then, which stands empty, heated and cleaned once all the children have moved out, and eventually deteriorates into a storage room for junk.

For what purposes the users of the unfounded area should be, I have not yet seen the OP explain. Thus it has remained completely incomprehensible to me what the mentioned house size is supposed to serve.