Assessment of Financing New Construction 425k € / Overall Financial Situation

Just a question ... 570 euros rent ... what size is the current property?

Exactly 88 sqm are currently in our attic apartment.

One must say that we live here in the countryside, the construction costs are perhaps not quite as high as in metropolitan areas and one is very well networked with people who can do the earthworks for a small price in various respects.

But that does not mean that you can afford "more house."

Only saving 15,000 euros and having 10 sqm less is not worthwhile in proportion.

Who is calculating the milk here? and if it is actually "only" 15,000, then that is 15,000 you could save. I rather see 100,000€ in savings, which also MUST be.

Of course you hope for better salaries in the future and I also consider that likely, but it’s all speculation and you can never really know.

Your salaries are those you have now and will accompany you for 20/30 years. If you eventually earn a little more gradually, then good... we all do. We all grow older. Then comes a new car, then the vacation... But that does not mean you can afford now what you could theoretically afford with a salary in 20 years. Furthermore: architect calculations are usually not adhered to: 20% more at the end is not uncommon. By the way, it really does not matter whether married or not: the bank needs 2 earners, 2 debtors, 2 signatures. They will get that.

The plan is to help with the bricklaying after work and on Saturdays, all electrical work done by my brother-in-law (a trained electrician), drywall, painting, floors, interior doors (my girlfriend's dad is a carpenter). Earthworks are done by a friend who works in road construction.
That's the current plan.

That already sounds good. I don't see the bricklaying happening, that will take you forever and a day. You'll do it in a week, and then you'll be done!
Every muscle will hurt, etc.

Of course, it will all take longer than if a contractor were involved. But we could temporarily move into my father's house, which is planned anyway. So additional costs for renting an apartment are basically not an issue.

Then the interest on the standby loan will eventually eat into it.
Just go to a bank and get some advice.

Um, very briefly. I can well understand the outrage of many users here. But setting that aside: Will anyone even find a bank that wants to finance this (without a golden parachute)?

Let's briefly summarize:
- External capital requirement does not match income
- 1 salary during probation period
- low standard land value
- unreliable architect's calculation
- non-financeable desire to have children
- certain credit affinity present (2x leasing; e-bike but I think it's employer leasing)

I think an AI will only agree to this if there is a valuable parental guarantee or unencumbered land charges on the parents' house.

…
That we are (still) not married honestly doesn't seem like such a big problem to me.
…

You could, for example, try to inherit a house from each other while unmarried. That's where it already starts.
I know a case …
If you can (still) afford a house with your income, the situation on the market can't be that bad after all :)