Floor plan of a small bungalow with a wooden facade

There was the desire to show the floor plans with 3 rooms.

No, that was the request to show your "original idea" once.

It could become the primary residence if the children take over our apartment. We would then be 50 years old and the children 20.

So you would be 40 and the kids 10. We have a total of 4 adult children but this constellation mostly takes place only in parents’ minds who cannot let go of their children. What if "they" don’t take over your apartment, then the house would not be the primary residence? I think you should go back all the way to zero and consider a more realistic life plan. Our children live spread out everywhere, it also changes from time to time and partly in faraway countries; the idea of an apartment swap is really strange. In our residential area, only young families live; the parents are somewhere else. Apparently, you are under pressure to build, maybe just sell the land again, maybe the timing just does not fit, or you build a house for now and only for now, with the option that the children/young adults can stay longer, but then with the possibility of a clear separation. Now you may still walk around the house in your underwear, with 14-year-olds and their visitors or permanent roommates that stops.

Doesn’t that apply to every construction project by people under 40, that you have to make long-term compromises?

Of course, but still I am building a house for someone who will soon no longer be there or as if they would not grow up and then behave completely differently in the house.

I hardly know anyone who builds new again at an older age. Everyone stays in their houses.

Yes, you are talking to some but just don’t know it, besides I wouldn’t need a comparison group for that either.

The worst-case scenario, like selling the house or having to move in early out of necessity, can never be completely ruled out.

There are thousands of worst-case scenarios; protecting yourself against three does not really improve the later hit rate. But I still probably haven’t fully understood. You live far away from the property? Do you live well? You don’t really go to a holiday home that is only 20 km away; it should rather be in a "holiday region" or where I like to spend vacations. Having two residences in parallel should, in my opinion, be based on a certain need; otherwise, you just have double costs without double benefit.

I'll show our house for two, upstairs (south) there was another room separated, but it was canceled again.

Are they supposed to set up a sibling shared flat there? They should first become independent and then they will move somewhere.

Could be, apartments can be terminated. Most people at that age would be grateful to find affordable housing in the city.

That is not relevant to the house, but to the property -
The utility providers have to get into the house. That costs your money, not the homebuilder’s.

Actually, meter locations take up space. Money is budgeted.

Seriously? Just build now: a bedroom with a comfortable bathroom and a large living area that suits a family and your wishes. Then a gable roof with a 30 degree pitch, where two children's rooms with a small shower bath fit upstairs. That is the cheapest form of living and offers a primary or secondary residence as well as space for togetherness later on. The children's rooms under the roof would then be an office, grandchild room, and sports. That would be the cheapest form of living that covers everything.

I don’t see any added value in going for the planned living space over 1.5 floors.

You are 40 and the kids 10 then.
We have a total of 4 adult children but this constellation usually only exists in parents' minds who cannot detach from their children. What if "they" don’t take over your apartment, then the house won’t be a primary residence?
I think you should go back way behind zero and think of a more realistic life plan. Our children are spread everywhere, that also changes from time to time and partly even abroad, a home exchange idea is really strange. In our residential building live only young families, the parents are somewhere else.

Please less speculation and life advice. I did not ask for that and there is also a lack of information for it. The house can definitely be a primary residence in any case. Whether you keep the apartment or not. Wanting to offer your children something that everyone else lacks is certainly understandable.

Apparently you have building pressure, maybe just sell the plot again, maybe the timing is just off or you are building a house for now and only for now, with the option that the children/young adults could also be there longer, but then with the possibility of a clear separation. Now you might still walk around the house in your underwear, with 14-year-olds and their visitors or permanent roommates that’s then over.

No building pressure at all and the plot will not be sold anyway, as it already creates enormous added value. The children and we are significantly younger than you assumed. If in 10 years they no longer want to go out with us, that’s perfectly fine.

Of course, but still I build a house for someone who will soon no longer be there or as if they would not grow up and then would behave completely differently in the house.

I already wrote that I need separate rooms anyway.

There are thousands of worst-case scenarios; securing yourself against three doesn’t really improve the later hit rate.
But I still probably haven’t fully understood. You live far away from the property? Do you like living there?
One doesn’t really drive to a holiday home that is only 20 km away, it should rather be in a "holiday region" or somewhere where I like to spend my holidays. Having two primary residences in parallel should, in my opinion, be linked to a specific need, otherwise you just have double costs without double benefits.

We live 45 minutes away. Very urban. The plot is close to the lake, very scenic. The contrast could not be greater. We currently go out there almost every weekend. Many people do that in our region.

I’ll show our house for two,
upstairs (south) there was a room sectioned off, but it was canceled again.

Very nice house! I like it and it resembles one of the previous designs, see attachment. The gallery is optimally used. The space for the TV does not work for me that way, though. The sauna is also great. So far I had planned it in the outdoor area.

The space for the TV doesn't work for me like that.

A TV is furniture, a young colleague said in the common room that the large right wall would be his projector screen. Our daughter said she would have a swing on the ceiling beam. The 4m extendable table is easily enough for 16 people. Everyone arranges things differently.

Isn't it true for every construction project by people under 40 that you have to make compromises in the long term? No house adapts to the use, and you should never build. I hardly know anyone who builds anew in their old age. Everyone stays in their houses.

Off topic: Rationally considered, a property is a consumer good like any other. As a couple, a small apartment is enough for me. As a family with one child, maybe a larger apartment in the city. With the third child, you build and move to the suburbs. When the children are out of the house, you build/buy nice again for two with a garden. At retirement, you move to a condo with a large balcony/terrace and good infrastructure.
That can be one possible path.

Meanwhile, it is also considered normal not to always stay in the same house. It is somewhat different in rural areas. But it follows the general trend towards change—residence, job, partner ==> changes are common today and are seen very differently than 30-40 years ago.

Yes, it may always cost some money. But that is the case with all consumer goods. And it is worth it for quality of life.

P.S. I count myself among those who change properties. Now in the fifth owner-occupied property, which always fits the life situation.