Financing: Our house construction project is scheduled to start next year

The question I ask myself:

Do you already have an idea of how big your house should be and how it should be "equipped"?

Maybe your requirements are relatively modest? This way you could already find out whether you could build your dream house for the price you have in mind or not.

For 330k you simply don’t get anything "special."

Where exactly do you live or where do you want to build? Prices in Germany vary from state to state.

I think managing a loan of 450k with a net income of 4k is doable but definitely tough. You are still young and can repay quite well for a long time as long as you don’t have children – but the salary increases you mention are not 100% certain either – that’s always the difficulty with it.

If I were you, I would first see what kind of house you actually want and then check how high the costs really will be – otherwise you will be disappointed in the end if you set a budget and can’t even come close to your expectations.

Then probably first secure a plot of land, pay it off, save save, and then in 2 years see where you stand job-wise and how the household budget/savings plan/repayment etc. is going.

Maybe your expectations are relatively modest?

She definitely wants to have a house; whether to build or not doesn’t really matter to her, but we have the same taste. We like modern houses and don’t want to buy a 20-year-old house for 400K.

It doesn’t read as modest. Furthermore, used houses are rejected.

For 330k you basically get nothing "special".

Then the incidental construction costs probably have to be deducted, which are not mentioned anywhere.

I.W. purchase prices. Should be due to declining demand. This will then also be reflected in construction prices

Whereas the average will benefit few. Especially where many want to live, demand will decrease the least. I would rather not speculate on significant savings there now.

Exactly where many want to live, demand will decrease the least.

Wrong.
According to studies, there are increasingly fewer immigrations (from abroad) into large cities and metropolitan areas. This clearly eases the market. Declining prices have already been observed for some time, for example, in the condominium sector in Düsseldorf. Additionally, the attractiveness of cities is no longer as high. Thanks to Corona, interest in living space is spreading over a larger area.
I no longer necessarily need to live in the metropolitan area if I only go to the office two days a week. I can also commute two days and still live in my small village.

The popular locations remain popular, that is true. But not at any price anymore, since there are alternatives.

Yes and no. Of course, it spreads out more across the area, but living is more than just sleeping. It starts with the fact that in the village the nearest cinema is a 10-minute drive away, there is practically no choice when it comes to kindergarten and school, and for concerts you’re happy to sit in the car for an hour. In general, you can also get around much better without a car in the city. There are plenty of people who find all of this important enough to stay in the city. And even professionally, the question is how widespread home office will remain in the medium term. Gossip by the coffee machine has its value, showing up in person is more important than actual performance in some jobs, and quite a few bosses probably have a problem with their team working out of sight. I myself belong to those who use the model of coming to the office only 1-2 days and moving far out. But I like country life and I know that neither country life nor working from home is for everyone. It will certainly take some edge off, but certainly not enough to speculate on falling prices now.

Whereas the average will be of little use to most. Especially where many want to live, demand will decrease the least. I wouldn't really expect great savings there now.

But conversely, further price increases? It should by now be clear that banks have long become more cautious with lending. Corona changes many things and accelerates everything – of course there will still be bosses requiring presence, but will good people start working for them? With "no mobile work," you will hardly get suitable people later on either. After 1.5 years, good companies will hardly reverse that but rather implement the experiences permanently. The next point is incomes – they will hardly grow broadly enough for the next few years to continue allowing 5%+ p.a. increases in construction costs and even more for land. Credit lines are not infinite, and trust in the payment ability of all players is simultaneously declining. Also, inherited unsanitary properties must first find a buyer so that "fresh equity" can go back into the cycle.

Moreover, there are the outlined "saturation tendencies" – for example, quite early for Hamburg. A lot of living space has already been created and continues to be created. If employees can live both far out and larger at the same time, the pressure will eventually decrease. Some move out, some stay, and construction continues both inside and outside.