Here in the forum, land costs are usually excluded. And honestly: recently, house dreamers who expect a monthly repayment of 700 € have never heard of development or incidental costs or have just come out of an apprenticeship with a temporary contract. The advertising lures with the interest rate. They inquire about the facts here and, of course, get the worst-case scenario presented. But better that than sugarcoating.
OP is asking about a situation where only one borrower comes into question. The bank will shake its head at the latest. Even if the construction costs 50,000 € less, it doesn't matter here. The loan amount is irrelevant, the financial situation is not given.
But I have to say, I know people who do it like this. As an example, a friend of mine: He earns 1,900 € net per month. She is on maternity leave (they had twins a year ago). 60,000 € equity. He alone services a loan of a total of 170,000 € with 630 € monthly. So he has paid a total of 230,000 € completely for everything (land, house, incidental building costs). In addition, there are about 25,000 € of own work. The garden was just done for an extra 3,500 €. Nothing has been done at the front yet.
The plot is a bit over 400 m² (purchase price just under 80,000 €), the house is a city villa, 134 m² living space with garage.