Offer comparison and liquidity planning for new construction, any experiences?

Prices in the West German metropolitan regions will collapse drastically soon.

Just like the interest rates will go really high as you predicted? LOL
First of all, prices have already come down - correlated with the increased interest rates. But unfortunately - for your as always unqualified statements - interest rates are already coming back down and there is still more than enough liquidity available. Prices in the metropolitan areas have stabilized and are starting to rise again.
Please explain why prices should collapse drastically?

Banks have special departments that practically market such distressed properties under the table.

Nothing works under the table at all. And the bank certainly cannot sell, only the owner can.

Now one more question that confuses me: The prefabricated house providers have their usual contacts with architects in the region themselves, and even when I pay them separately, they presented this as the standard procedure. Do the prefabricated house providers only say this so that no competition is requested in the first place?

You pay, but the architect builds and designs the house for the prefabricated house provider. Yes, this is common - whether it makes sense is another question. This way, as a provider, you have everything from a single source (no hassle with rebellious customer architects) and you can even sell this as an advantage.

We are on the brink of a pretty severe crisis, let's see where the journey and the prices will go.

As shown to you above, the storage does not pay off. We have a photovoltaic system with a 10 kWh storage, which was well subsidized back then with KfW40Plus. We have 2 electric cars and with the photovoltaic system, it works great. With about 25,000 km/year, from around April to October we do not need any electricity from the grid and only use public charging stations if we occasionally drive farther away. The battery storage does not help you at all regarding the electric car. I would rather fully cover the roof and only add the storage if I enjoy this technology. Besides the financial calculation, there are other reasons for it. Many things are nonsensical from a calculation standpoint, but maybe it’s fun; I like it.

We have been hoping for years, but unfortunately nothing really gets cheaper. And it will still take a while until the boomers die out and many houses become available.

Uffff. There are certainly some thoughts. I enjoyed building when my parents were still alive.

Just wait. Prices in the West German metropolitan areas will soon collapse drastically.
We are currently sliding into an existential economic and liquidity crisis of unimaginable magnitude.

I have been reading such crystal-ball fantasies for what feels like 100 years now and it has always turned out differently. Of course, many things can happen, but to base my life decisions for my family on such a bold thesis...? Then completely different decisions would have to be made because we will soon be burning up, flooded, and/or overrun, and then children won’t be considered at all. I understand that you are overwhelmed. I would be too with today’s extreme excess of information.

We only wanted to commission an architect when we know whether we can build at all.

and have a suitable plot firmly in sight and have basically clarified the financial situation (see note ). You always need a buffer anyway. Without a plot option, this doesn’t make much sense at the moment because it can immensely influence the costs. For your fundamental decision, the above rule of thumb is sufficient, which I would set even higher. If you then actually have money left over, get yourself a hot tub in the garden. We were recently in Tübingen and I liked it very much there. Nevertheless, having a beautiful and comfortable house (not size) would be more important to me and I would rather consider where I can realize that better in my situation. That photovoltaic panels are mandatory does not matter; you should have that anyway with new construction in 2025.

We have been hoping for that for years, but unfortunately, nothing really gets cheaper. And it will still take a while until the boomers die out and many houses become available.

You mean the houses that the boomers mostly built themselves from 6 a.m. alongside grueling jobs and running after children, raising them up only with their own efforts? Is your sentence now irony or just simply disrespectful?

Please explain why prices are crashing drastically?

A short quote from Focus:

The fat years are over Rößer, who has spent her entire life in Wolfsburg, feels the great uncertainty in the city. VW workers called her, determined to "sell their houses before they lose value," she says in an interview with DW. Other customers canceled their purchase contracts at the last minute. "People hesitate to buy a new house and want to hold on to their money until they know what VW decides," she says.

I don't need to write more about it now. And the real economic downturn hasn't even started yet. It will be exciting!

I don’t need to write more about that now.

If such are your sources for facts, then I apologize. It’s not your fault.

But it can’t hurt the overpaid employees of VW to be grounded in reality. VW is a good example of how things go when the state interferes in economic matters (even if VW’s management has not exactly covered itself in glory, but the top management is still held by the state of Lower Saxony). Sorry for the employees, but they have a special status in Germany.
"The wages at VW are higher than in the rest of the automotive industry. Good for the workforce, bad for the company."
"With a median income of 5238 euros, Wolfsburg is one of the wealthiest industrial cities in Germany. Only Ingolstadt, where the car manufacturer Audi, which also belongs to the Volkswagen Group, is based, is richer.”

And on the topic of the depreciation of houses, by the way, like the other quotes, also from “your” article:
“The real estate agent shows a bungalow-style house, which in her opinion is typical for the homes of many VW employees in Wolfsburg. A room divider, petrol-colored PVC floors, and yellow kitchen tiles date back to the time when many of these houses were built in the 1960s.”
==> These houses have lost a lot of value in all cities of Germany in the last two years. They are old, unrenovated, energy guzzlers. Nobody wants them—economic crisis or not.

Oh, you can write even more. It’s always an entertaining read from you. Perfect for falling asleep.