Is house construction financing possible at all?

But the whole getting younger thing is just a phrase.
My parents built at 60/62. We are currently at 41/43.
I also advise against building in your situation. I imposed the rule on myself: being able to spend 20% of the actual income on the installment, I won't go above that. And then last year it was time. Fortunately with very good interest rates for the term (1.2% over 15 years, 100% financed, incidental purchase costs covered with equity).

With 20% of income for a property and 100% financing, you either have to earn above average or build significantly cheaper than average. Of course, this is very healthy, but for many home builders I consider 20% almost unfeasible.

Even the old one-third rule has long been barely possible anywhere, now even less so. What really matters is what remains in the end. 50% of the income with €3000 left is simply better than 30% of the income with €2000 left

1000 EUR for a full-time position is less than minimum wage.
Do training at Dekra, for example, as a daily companion for seniors and/or disabled people.
The training lasts 3 to 4 weeks.
With this certificate, you can get a job almost anywhere, full-time or part-time. Then your wife earns at least 1500 net full-time. Not to mention the good feeling of helping elderly people.

Otherwise, besides the financial side itself (improving income and equity, "hoping for better interest rates"), it might also be worth reviewing your own expectations for the house. So looking around the existing stock is an option, and if building yourself, also consider how much we really need individually. Many builders of detached single-family homes have a certain amount of frills. That sometimes strongly influences the impression (also regarding normal prices). Do you need that or where do you stand on that?

Would smaller also be an option (there are also good compact floor plans), a townhouse would also be conceivable, do I really need a garage, can I also manage with the basic standard or is it foreseeable that I want more in 50 different places.

So, people say prefab house builders are not necessarily cheaper, but if you can come to terms with a promotional house without changes, which might also be a bit smaller, then I believe some are not outrageously out of reach. (Still be careful with teaser prices if you ever google. They are often from the top edge of the floor slab, which should not be underestimated, and also what is included as standard afterwards varies greatly. So don’t underestimate the additional costs that are not mentioned.)

At the moment, I still don’t really see it as feasible, the interest rates are hitting very hard right now. But looking around while you continue to consider it doesn’t hurt ;)

The old one-third rule has already been hardly possible anywhere for quite some time, now even less so. What ultimately matters is what remains in the end. 50% of the income with 3000€ left over is simply better than 30% of the income with 2000€ left over.

Their basic meaningfulness is now quite clear. That deviations upwards are possible for very high net incomes was ultimately always the footnote to the rule of thumb. Therefore, saving & improving income is certainly not bad advice. Interest rates are already very high anyway, and the asking prices on the existing market are by no means where they will end up given the interest rate level. The real estate market is relatively sluggish. Therefore, I consider waiting, observing the market & building equity to be the best approach (despite inflation). Today, only those who have a lot of cash & truly secure income components can build. Buying land and hoping for falling prices also seems too risky for the original poster.

Otherwise, besides the financial side itself (improving income and equity, "hoping for better interest rates"), it might also be worth checking your own demands for the house.

I would support that too. Acquaintances live very happily as a family of four in a Flair 113 with just under 30 sqm less than your desired house, completely without a garage. They consciously chose a smaller house with a relaxed payment rate. The income is similar to yours, but the financing was done before the recent interest rate hikes (without significant equity except for the incidental costs).