I have read through all the answers and there are really many valuable ideas there. What I take away for myself is: If it doesn’t work financially with a plot of land and a building of at least 90-110 sqm (because anything smaller as a detached house is completely uneconomical), maybe a permanent pitch with a high-quality mobile home ([there are some nice options around 50 sqm for singles and couples, up to 100,000€]) could be a viable alternative (perhaps not economically, since you don't create value like with a property). I first bought the picture book from Thomas Drexler about houses under 100 sqm. My idea has not been completely abandoned yet but I now see it a bit less dreamily financially, the likelihood of implementation is rather low. But last week I already visited a plot of land.