Full financing or saving?

The questioners are in their mid to late 20s and, as far as known, without children. My personal advice (from a slightly older perspective) would be to set goals and prioritize them (the latter is very important):
- Own house with everything that goes with it --- Yes/No
- Children, and if so, how many --- Yes/No
- Professional career --- Yes/No
(Career in the sense of career, not as this term is used in an inflated way today...).
And then you organize your life accordingly. For example, if the house is set as priority 1, then from the 5700 euros net, 2500 to 3000 euros must be saved (savings account, fixed-term deposit ladder). If the career is priority 1, I see owning real estate more as a disadvantage. Well, and if children are desired, then I would have them first and then find the suitable house a bit later.

PS: The list of goals can of course be supplemented or changed arbitrarily.

Hello,
at least I would save for the ancillary construction costs, notary/taxes, and a buffer of €20,000. And I would not build before I HAVE children. From a simple consideration: neighbors of ours built with 2 children's rooms. And then she didn't get pregnant. Everyone asked, and it was really hard for the two of them until they were finally able to have children with great effort. Or the other way around: you build too small now because you only plan for 1 child, then it’s so cute and smells so good and - bam - you want more...
With your salary, I would probably also build bigger and more expensive than I did now, so I would wait at least another 1-2 years, save, keep a household budget, take South Sea vacations, get married, plan children, and collect ideas for a house. If the perfect plot of land appears during this time – grab it.
Best regards