Use garage as house/bungalow?

Without going into the idea in detail: the budget will not be sufficient.

And no, rent is not wasted money. Renting even offers a certain level of security.

Find yourself a small apartment or a shared flat room, maybe you can also find shelter with relatives.

But there are after all also these microwürfel for example. With 10 - 20 sqm or so for 20000 then it must somehow be possible to realize something like that individually and in the form of a house? The difference would only be the design and the room layout.. well whether 15 or 30 sqm is not a huge issue the luxury I can do without if I can enjoy the luxury of having my own home and letting my soul unwind.

... if I can enjoy the luxury of having my own home and letting my soul dangle.

I know you don’t want to read moral sermons, but when I read that, I get plaque!

I don’t know anyone (myself included) who didn’t have stress with society and family between the ages of 16 and 20. But sooner or later, you realize that retreating to lick your own wounds doesn’t help. As you can read here, the crazy idea gets you nowhere because without money, nothing works! There are always ways and means to come to terms with society and family; most problems are caused by oneself. Either you stand in your own way or are just too stubborn.

At 18, one should have other goals than "letting the soul dangle."

This is not about some pubescent 18-year-old, this is about me, someone who can no longer withstand the pressure, and not guilt pressure or parental pressure regarding "You'll never amount to anything" or anything else, this is about me, about an 18-year-old who has to deal with the suicides of good friends, extreme violence from parents, various "street" problems and more every day. I should have realized that everyone here sees the typical 18-year-old rebel in me. Sorry, I should have expressed myself differently. This is not about a bit of independence but about a possibly livable life. What I just said no one really needs to know, but I probably won't get answers or users who take me seriously any other way. And please, no lectures about the youth welfare office and this and that, believe me, it doesn't help. I just want to get away. Can you recommend condominiums? They are also affordable here.

Then do it like every 18-year-old and get yourself a shared flat room or a small apartment! With 15k€ you won't get anything. Period.

...It should have been clear to me that everyone here ...

Clear case of misreflection and exaggeration... so far I have only written something off-topic here, everyone else has addressed your question. And THAT'S exactly what I mean: creating problems where there are none, making oneself the center of society and licking one's wounds.

Take, as others here advise you, a room in a shared flat in another city and do something... You can avoid rough neighborhoods, then you have a few problems less as well. Choose a realistic goal, for all I care also your own house, after all you have to work for a goal in life. Good luck!