Construction costs are currently skyrocketing

I also believe that the interest rate will continue to rise. But not ad hoc induced by the ECB decision.

P.S. Anyone who wants to stay informed daily about the development should google "Swap Mid 10 years." finanzen net has the 10-year rate daily dz hyp has all rates from 1-30 years at a glance daily boerse manager magazin 10 years with charts Swap Mid rate = refinancing rate for banks (simplified)

Of the 1250 pages here, about 98% are just far-right nonsense, unnecessary discussions, or posts from pseudo financial experts. It really gives you a headache.

On the actual topic:

Window offer in April: €30,000, window offer in June: €37,000, window offer in September €36,000.
The company is booked out until early February.

I agree 100% with the first part of your statement.
A friend who is a construction contractor mainly working on single-family/semi-detached houses hasn’t received any notable inquiries for 8 weeks and is still fully booked until next summer, after which things will get uncomfortable. Our house bank’s statement is that currently there are no financings for new builds. We are now only buying the land this month and hoping for better times.

Sign the first part of your statement 100%.

And if everyone were as active as you, the forum could be closed immediately. So, keep a low profile.

The fact that so little is written about costs here is already a statement in itself.

Available for 60.60 at the second Google result after the big river (105€)...

This is a double-edged sword. You can certainly snag a single item cheaply somewhere online at short notice. The problem is that many are tied to a general contractor (GU) and thus to their sources. Very few still build their house almost entirely by themselves, and then nobody probably buys the materials just-in-time either.
Perhaps the wrong example was given here. Prices here in Germany—for almost anything—have long been detached from the (world) market price. The best global example of this is raw material prices like steel, crude oil, etc. My general contractor now wants almost €500 more per ton, even though the steel price is currently at the level it was when the offer was made. But the steel that is currently ready in the yard was bought months ago when it was at a high. Surely there is still a bit of "filling pockets" involved. But I would rather attribute these price distortions to the bullwhip effect.
Someone from the forum once mentioned the "rocket and feather" principle here. It hasn’t left my mind since, as it describes this situation most accurately.

And if everyone were as active as you, the forum could be shut down immediately. So, keep a low profile.

Man, someone is really angry. Slept on the couch again? :D