Floor plan of a multi-family house with 4 residential units

That is why much less is being built for now. The developers can hardly calculate the costs anymore and buyers cannot afford these prices at the current interest rate. If the interest rates stay the same or even rise, which I assume, prices definitely have to come down... You used to build such houses a few years ago for 600k to 700k.

Yes, that is correct. I have also been observing the market in our small town for many years. Ten years ago, the square meter from the developer cost €1800 turnkey, and the apartments were all sold only after completion. At the topping-out ceremony, there were still some available. Five years ago, the price was around €2500 per sqm. Two years ago, the apartments then cost about €3000 per sqm, and a year ago €4000 per sqm. In both cases, all apartments were sold before construction started, i.e., two years in advance. And now we are at €4500 per sqm here, and for a current developer project, which will be finished in half a year, more than half of the 36 apartments are still available, and this has been the case for months. Nothing is being sold here anymore. Because if you imagine this as a graph, prices have risen above average in recent years. But when you pin a 2.5 times higher price than ten years ago to the offer, it was clear that the price rally would end at some point. That it ends so abruptly now is, of course, bitter for the projects under construction... but it definitely will not get more expensive; whether it gets cheaper we will see, I don't think so.

and then I have a new building and am the boss on my property and don’t have to coordinate with other owners etc.

But don’t forget that then you are a landlord and still have tenants in the house. You have to expect that on TV night someone will ring your door because of some problem. I have another idea. So far the apartments have always been just on the ground floor and upper floor, maybe an apartment can also be sensibly accommodated in the basement. The view of the parking lot is not great, but the slope should roughly be enough for windows without a light well. Then you could distribute the apartments 2+1+1

The idea is not bad at all, but I doubt whether the demanding Munich rental clientele would want to live solely in the basement for 15€ cold per m2. What I do think would fit quite well, however, is a kind of maisonette in the basement. The small 3-room apartment could be turned into a spacious 2-room apartment on the ground floor + 1 room in the basement with a bathroom and storage room. This would definitely provide about 90m2 and could save some of the unnecessary basement area, since with 4 apartments + technical rooms + bicycles you would actually only need half of the actual basement space.

I would not only focus on Munich city escapees. There are also people who have lived in the area before. One consideration would be to make it a one-room apartment since you only get daylight from one side anyway. Perfect for young people who no longer want to live with their parents but don’t feel like living in a shared flat. If you stay under 25 sqm, it would only need one parking space ;)

But then the ground floor apartment would be 150 m2 and the TE only wanted a 3-room apartment. I find 2x 2-room apartments and 2x 3-room apartments best suited to the TE's wishes. Because this way you also have a decent rental yield and do not build an apartment that you would never be able to rent again at a good price with 150 m2. The more compact, the higher the rent per m2. So better more rooms on a smaller living area than the other way around.