Is financing for house purchase / house construction feasible?

So you are claiming that all normal homebuyers of developers (semi-detached/townhouses) are unhappy in the long run? Well planned, they are completely sufficient. The rooms won't be the size of a ballroom, but that's not necessary to be happy.

And additionally. How unhappy are the tens or hundreds of thousands (or even more) of renters with 2 children, who in a 4-room apartment only have 100 sqm with two kids - but have to do without a garden?

Well, unhappy is a poor choice of words, sorry. Of course, someone with 2 children can be happy in 80 sqm.

What I’m getting at: I acquire property in which I might live for a lifetime, go into debt for a lifetime, but have to give up what maybe bothered me forever in the rental apartment? At least that’s how it is with us.

With such a project, I wouldn’t want to skimp. That’s just my opinion that I want to suggest to the OP.

Financial pressure often makes people inventive, which is not always positive. As I said… it always depends on what you want to do without or not. Then better save for 2 years, get 30k more and have 20 sqm more (as an example).

I know enough people I know who made exactly this "mistake" and now wish they had much more space.

Just as an example: “You’re having a third child, then what?” Then there really is no free room left to plan a child’s room.

Well, unhappy is a poor choice of words, sorry. Of course, someone with 2 children can be happy in 80m². What I mean is: I acquire property in which I might live for a lifetime, go into debt for a lifetime, but have to give up what might have bothered me forever in the rental apartment? At least that's how it is for us. For such a project, I wouldn't want to economize. That's just my opinion that I want to suggest to the OP. Financial distress often makes people inventive, which is not always positive. As I said... it always depends on what you want to give up or not. Then better save for 2 years, get 30k more and have 20m² more (as an example). I know enough acquaintances who made exactly that "mistake" and now wish they had much more space. Just as an example: "You get a third child, then what?" There really is no free room left to plan a nursery.

The difference between being able to afford something and wanting to afford something is huge. We (3-person family) currently live in 70 sqm without a garden/terrace. 100 sqm apartment with a garden share would also be enough for us. Unfortunately, prices here are so high that building is more worthwhile, especially if you already have a plot of land. We could also afford an apartment with a 1,700 € warm rent. But why, if you can pay the interest + incidental costs for a new build instead.

This "what if" game is futile. What if both children tragically die? What if you separate? The smaller affordable house might possibly have been kept, the larger one not. So it's really not an argument.

And then the question: what to give up sooner? Generally give up a garden? Or 5 years of a mud pit in front of the house because paving is expensive? Or give up roller shutters? Or give up... yes, give up what exactly? You only build once. Then also give up a few conveniences in favor of a larger hallway or an extra room? I don't know.. But you wrote it correctly: this point is important to you. For other people with a tight budget, it might be much more important to afford something of their own and nice.

Everything is completely understandable. I just wanted to present my point of view here so that the OP also knows that 120m² single-family house is not the same as 120m² apartment.

Often there is also a basement room with about x m² included, no technical room, etc... That can of course be very misleading and no one wants to be disappointed when the house is built and they start thinking about how to fit everything in here.

Due to the current low interest rate phase and at the same time high construction costs, it is simply a difficult undertaking... Very, very hard to do the right thing. One definitely has to make sacrifices; everyone has to decide for themselves what they are willing to give up.

As I said, I understand all the above-mentioned arguments! I simply hope that the OP then makes the right decision for their individual situation and considers all factors.

The question is, how long do you want to wait. Saving every year also means restrictions in the rental apartment and one year less until the children move out. When they have moved out, most houses are too big anyway.

We deliberately set our budget low and built rather small with 125m² to avoid any restrictions through financing. Of course, in hindsight a few more square meters here and there would have been nicer and one or the other upgrade could have been taken later as well. But nothing dramatic. For that, we are already halfway through the financing after just over 7 years.

The house is everyday life and the bigger it is, the more time you need to clean. That does not make you happy. It is nicer to sit on the terrace with a glass of wine or beer, put your feet up, or travel the world.

In the relation, however, a larger house is also cheaper per square meter