Build a house, buy a house, or...?

Hello everyone,
I would like to sincerely thank you once again for the many suggestions and tips.
We were at the model home park in Mühlheim-Kährlich on Friday and saw several houses that we really liked (Hanse Haus, Fingerhut Haus, Fingerhaus, Büdenbender). We had some informal conversations everywhere and took brochures with us.
Currently, I actually tend to wait and save equity, even though it is of course practically eaten up by the construction price control.
We will certainly have a longer consultation with some of the companies, also with a general contractor (I just have to find one for my region) to find out concretely what we really want and what it costs.
People often talk about 2000€/m2 here, which is of course a considerable amount. I do think we would like around 150m2 plus a cellar. I know nowadays houses are often built without a cellar, but I find it very hard to imagine. A friend recently built a prefabricated house without a cellar, but on a very large plot and with about 137m2... and I really have to say, that would be too small for me. On the ground floor there is a relatively large utility room, which makes the living room and kitchen relatively small.
The costs amounted to about 400k including land (250k house + incidental costs + 90k plot of 900m2), almost finished stage. Only floors and walls were done by themselves. There is still some money left for landscaping and carport. And the family has a somewhat higher net income than us.
So I almost believe that if we really want to build, we will need an amount around 400k (without land price, which we already have). And then I still don’t know if it is worth it to me, even though I can be sure that in a few years, a certain amount will flow to me and my sister through the sale of our current house by my parents. My wife and I just need to think about it longer and also get one or two plans and consultations from the companies.

Thank you for the update on your considerations
Here’s a thought on the subject of the basement:
We also thought that only the attic and utility room might be missing and that we couldn’t afford a basement. Our alternative now looks like this: we will add an extra room to the kitchen and then use it as a balcony on the upper floor. This way, we have a bit more usable space at significantly lower costs than we would have had for a basement. You can choose the size and shape of such a room quite freely. Ours will be 4×5m

Thanks for the update on your considerations
Here’s a thought on the subject of a basement:
We also thought that only the attic and utility room might be missing for us and that we couldn’t afford a basement. Our alternative now looks like this: we are adding an extra room onto the kitchen and then can use it as a balcony on the upper floor. This way we have a bit more usable space at considerably lower costs than a basement would have cost us. Such a room can also be chosen quite freely in size and shape. Ours will be 4×5m

That’s not a bad idea either. Thank you very much!
Are you building solidly or a “prefabricated house”?

My basement.

My basement.

So attic and the area under the stairs? We currently have a basement and I’m just wondering where to put all that stuff if we didn’t have one anymore. Bicycles, lawnmower, laundry, tools, etc... I know there are solutions for everything and Yosan’s idea isn’t bad either. Let’s see... sounds stupid now, but how do I go about finding smaller house building companies (solid construction) in my immediate area or the so-called general contractors? Companies like Fingerhut, Büdenbender and Weberhaus are basically just around the "corner" ...

no. The attic. And to make it easy to get there, three and a half extra for stairs instead of a floor hatch.