Additional costs for residential units

I can only admire your tirelessness and must unfortunately admit for myself to capitulate before the genius of the OP and probably cannot do more than wish him all the best in this case.

I can only ask once again where the reason for such a devaluation of my idea can be found. I have been explaining for quite some time what I want to do and how I come to these conclusions. I keep saying that I am neither infallible, nor a professional, nor 100% fixed in my decisions. I very much welcome coherent counterarguments so that I can go back into planning based on them. But I do not read any concrete counterarguments or they have been dispelled or still need to be checked on site (for example, the important note about parking spaces). Or did you have one now that I overlooked? If it is so simple and I am miles away from any reason in boundless stupidity, then please summarize briefly and conclusively what delusions or misplannings I am falling for here. That would help. But mocking together instead and dismissing it, unfortunately, does not help.

Here is also a brief sketch of the roof (pitch 35 degrees) and an attempt to show at which roof pitch which height is reached. As mentioned before, insulation/roof thickness has not been taken into account here so far.

In my opinion, there can be no talk of only 20 square meters of area in the attic.
Am I overlooking something here? Or is the error in your calculation?

With a roof overhang of 1 meter

The roof OVERhang is practically (actually) irrelevant.

With a slope of 35 degrees, you roughly reach 1.5 meters of room height after about 2 meters of roof slope.

In your statements I at least cannot see what exactly is supposed to be wrong with my estimate.

According to your sketch, which you can clearly see, you are planning a knee wall for your roof. Roof beams normally rest on the outer wall. In your case? What kind of structure is that? With the knee wall you are of course raising your roof by about one meter/70 cm or so.
The roof overhang is shown in your sketch, the beams lie over the outer wall, so practically on a knee wall.
But you keep coming up with new surprises ;)
Anyway, I forgot earlier that with a knee wall of 1.50 meters no second escape route is possible because it cannot be reached.

The roof overhang is hooked according to your sketch, the beams lie above the outer wall, so basically on a knee wall. But you keep coming up with new surprises ;)

To be honest, these were no surprises for me. I had mentioned the roof overhang and am far from being proficient with the terms. From a layman’s perspective, it was logical to me that I plan the roof starting from the overhang. I just can’t imagine it differently right now... I can’t start the roof on the walls and then somehow build something a meter in front of that. But probably that’s possible and I just don’t get it. For me, a knee wall always meant raising the base walls, that is, a later placement of the roof somewhere within the attic. In my case, it’s just a roof overhang. Of course, that results in a similar effect afterwards (the roof is higher and the space inside is larger). To ask specifically again: Was my rough area estimation of the attic correct for such a roof design? I couldn’t really follow your figures, even with a roof starting directly on the base walls. And if it doesn’t work that way with the roof overhang, how do you do it if you want a roof overhang? The slope must then start at the "tip" of the roof, that is at the overhang. And not only at the base wall. Right?

At a 35 degree slope, I reach a room height of 1.50 meters within a few meters (from there I would want to set back the walls, so start the room). One meter further, I am already at about 2 meters room height.

However, that is not permissible for an escape route. The fire department cannot place a ladder there, nor can the resident get outside through such a high window. Just plan a dormer projecting forward, you will need it.

If it’s so simple and I, in boundless stupidity, am miles away from any reason, then briefly and conclusively summarize which fallacies or misplanning I am falling for here.

I’ll answer for 11ant: You feel like the third person this week who, with Pioretten thoughts, stubbornly plans a granny flat just to at least theoretically get a taste of building a house. We’re not stupid here either, even if some like to pretend that way. Arguments come up… hehe, hopefully 11ant has documented some of it. We are certainly not all-knowing, I already said that. But many things we know, we have read up on it here and know a bit. If the OP then has a "but" on every page here, believes nothing, just brings up the mentioned Pioretten, then you can read that by now. Normally one no longer deals with those who want to use our tax money for something that then is not to be used as the KfW sees it, namely to create living space. I’m replying to you because I can’t really assess your intent. But I can already estimate the increasingly dominant role of the flat: the house will get even higher, and the house will get a very expensive roof structure, which already eats up the subsidy. That’s already the somersault with a head landing and the ongoing headaches predicted beforehand. My personal opinion: the idea stinks if I want to build and have someone else living above me.