But is it better to buy a house?

I think the OP is definitely helped by providing counterexamples to the thesis put forward here "Forget it.

But only if you also include the year of completion, the size (number of floors/roof type), the area, the own labor input and, for example, the level of equipment. You don't want to compare apples and oranges. We have had this here repeatedly; building just 1 or 2 years later made the area more attractive (=higher land costs), increased construction prices, or the next person didn’t have an electrician in the family who did the electrical work at a family price.

But only if you also include the year of completion, the size (number of floors/roof style), the area, the DIY work, and perhaps the level of equipment. So that apples aren’t compared with pears.

We’ve had this here again and again, building just 1 or 2 years later made the area more attractive (=higher land prices), raised construction costs, or the next person had no electrician in the family who did the electrical work at a family price.

Yes, that’s clear. This was just meant as a brief comment and not an attempt to divert the discussion.
I think you really have to be very careful when you repeatedly throw blanket statements like “nothing below 350k,” “2,000 euros construction cost per square meter—rather more,” or “you must have at least 4.5k net, otherwise forget it” at rather inexperienced advice seekers here regularly. I used to believe such things here at the beginning and mentally started to question our project, but now that I have a more detailed overview of costs after moving in, I see that my wife and I have stayed well below these exaggerated forum figures and our house has still been standing since early October (and that’s not in the middle of nowhere). And I say, even in the Cologne commuter area, it will be possible to stay realistically below 350k. It’s undisputed and can at least be assumed as known that it won’t be the 180 sqm hut from Kampa on an 800 sqm plot with a view of the cathedral. But before any half-truths become entrenched, I think it is in the interest of a forum that those who have up-to-date firsthand knowledge also share it here. For those who find this unnecessary, the use of the scroll wheel on their mouse is recommended.
Have a nice Sunday!

Yes, that's clear. This was meant to be just a brief comment and not an attempt to turn the discussion.
I think you really have to be very careful when you regularly throw blanket statements like "nothing goes below 350k," "2,000 euros construction cost per square meter - rather more," or "you need at least 4.5k net income, otherwise forget it" at rather inexperienced people seeking advice here. I believed such things here in the beginning as well and mentally started to question our project, but now that I have a more precise overview of costs after moving in, I see that my wife and I have stayed well below these inflated forum benchmark figures, and our house has been standing since early October (and not in the middle of nowhere). And I say, even in the Cologne metropolitan area, it will be possible to stay below 350k with realistic expectations. It is undisputed and should at least be assumed as known that it will not be the 180 sqm Kampa hut on an 800 sqm plot with a cathedral view. But before any half-truths become entrenched, I think it is in the interest of a forum that those with current firsthand knowledge share it here. For those who consider this unnecessary, I suggest using the scroll wheel on their mouse.
Have a nice Sunday!

Well written!
It is extremely unfortunate that it feels like the same people always pick apart all the questions/statements asked and actually provide no help. This constant "for that money it doesn't work, not with that income" is just annoying!

That really annoys me here in the forum.

It solely depends on the location. For all reasonably sought-after locations, the statement that you cannot get a detached house with 150m²+ and a plot for 350,000€ is simply a fact. Variables are location, size, and own work. If I already have to pay 200k for the towel plot, I don't need to think further with a budget of 350k.

Forget it. You can't get a house including land and additional costs for 350k. Your brother-in-law, as an architect, should also know that.

I have NOT asked him yet.