Floor plan for a single-family house with 4-5 children's rooms

@ moo Regarding the QM and specific numbers, my goal was to have a starting point, also with a limited budget in mind. There is always room for maneuver in both directions. I think over time one should develop a sense of what one personally needs, what one values, or what can be neglected. At the beginning, however, I found it very difficult to imagine anything from the numbers, I measured a lot in various houses and was gradually able to develop something of my own. Therefore, first a standard proposal and some suggestions outside the standard to engage with it yourself.

That was more of a general observation in the construction industry, there are often fixed norms in mind (the living area MUST be this big, without this and that it won’t work, etc.). I think many in this industry could use some creativity, but you just want to push your standard solutions. And there are also people who say, how can you only build an 11sqm children’s room, poor kids (read that the same way), so I just wanted to point out that there are (if necessary and desired) ways to partly bypass these norms :) But to get an overview, it certainly doesn't hurt to first think in "standards," you are definitely right about that.

220sqm x €2500 = €550,000

Therefore, I already hesitated a bit regarding areas with corresponding suggestions for implementation ;) with the result of €50k additional free capital. One will get rid of it quickly enough...

I will try to create a concrete draft using the tips. Thank you very much for the many pieces of advice. 600,000 at least do not seem entirely far from reality. There is a bit of leeway; in addition, the price of our current house is calculated very low since I do not want to plan with money that is not yet available. Are these 2,500 / sqm realistically achievable according to experience, or will it always be 2,700 or more? Are the KFW subsidies that have been discontinued included in this value?

these 2,500 / sqm are realistically achievable based on experience or is it always 2,700 or more?

Depends on where and how you build. I can't quickly find your region. Basically, it's more expensive in the south. And the higher the standards, the more expensive it is as well.

Are the KfW subsidies, which have been discontinued, included in this value?

No. KfW works/has worked in a way that you apply for a loan for the entire amount and one component is the loan from KfW, the rest from a regular bank or other funding sources (you can check in your federal state, maybe there’s something for families with many children). Usually, after about 2 years you get the repayment subsidy on the loan.

So it surprises me that everyone here considers this feasible without any reservations.
I calculate:
220 sqm x €2500 = €550,000
Additional building costs €40,000-50,000
Kitchen and furniture €15,000

And already, without any outdoor facilities, I am right at the €610,000 limit.

It was already pointed out at the beginning #4.

Currently, with 220 sqm, you'll already exceed the €610k, without additional building costs/attic/outdoor facilities etc.

Write down your exact requirements, including space requirements.

Exactly that and nothing else. Although I would call them wishes rather than requirements. (They are easier to remove. ;) )