What loan amount is realistic for house construction?

Hardly believe that there is something uniform?!

According to our bank advisor, his bank also assumes 1400 euros for living expenses. Other banks apparently sometimes calculate with "only" 1000 or 1200 euros. However, as far as I know, this does not include the additional costs for the house, but really only things like food, clothing, etc. Accordingly, the possible installment payment for the loan does not result after deducting the 1400 euros (1000/1200 euros). If you include your girlfriend in the loan, it would probably look better with a loan. We even have less combined net income than you (by 3450 euros) and would probably have gotten a loan amount of 320,000 euros from the bank with 80,000 euros of equity and an existing plot of land. Whether one then wants to manage a loan of that amount is another matter. For us, the new construction project is too risky and the concern too great that the costs would exceed the budget during the course of construction. Therefore, we will rather resort to another alternative.

We now have (it was less when we moved in, about €3000) a household income of just under €4200 for 4 people (including 2 children). Repayment to the bank is €1050, with our equity we were only able to manage a bit of interior finishing and incidental purchase costs. The loan amount was €239,000 and then we had to refinance another €8000. And even if we would get more today (our bank uses 100 times the monthly net income as a guideline), we are really glad we did not buy more expensively. The house costs a considerable amount of money, it is not comparable to an apartment. There is always something to do here and there, something for the garden, something else, and normal life with costs for car, children, etc. comes on top of that... and we are not finished yet. Even 2 years after moving in, we still don’t have money for the kitchen door, the new front door, or the last 3 old windows, the cellar door, and so on. We do everything nicely in order, by priority, we are making progress, but the money originally estimated for renovation was already gone before moving in. That’s not terrible, because the important things were finished and the old doors will last a few more years. But there is also a difference between "we leave 3 old windows in for now and do them later" and "we live for 5 years basically in a shell with a muddy wasteland in front." Really think about it calmly, get advice. And don’t ignore the warnings here. There are many people here who really build big and expensive and consider that the minimum, but most are well-intentioned advice from people who have already built or bought.

Yes, but some who built expensively handled it like

How did he handle it?

He did write: saved for 15 years and increased the income.

Well, aside from the fact that this project won't work out like this. The advice to save for 15 years and increase your income is already somewhat cynical.