Which companies build affordable expansion houses?

It's quite simple, ask the bank what credit they will give you and then check (get offers) how much house you can get for that.

I had the impression that OP wrote something about a 180,000 loan, also that he saved 10,000 (which he hadn't dreamed of before)

Oh people, please stay factual. One should not make fun excessively. The OP has certainly understood the objections and will hopefully take them to heart.

most people here are so bitter... unbelievable.. I think I'll look for a friendly forum where you can dream and eventually make dreams come true....

Well, let's say the forum is rather cautiously optimistic and if you don't pay for a little house out of petty cash, you will first be ripped apart. After that, it is up to each individual to make the best of it after the first rough landing.

The forum participants here only want to prevent illusory dreams from leading one to rush into misery. Therefore, better to be a bit pessimistic and not ruin life than to buy/build a house and lose everything because one approached the matter too naively.

Air castle forum...

and by now people are diligently saving, already 12K€

very commendable and phenomenal, saving 2000 within 10 days

Your statement that you are a low earner is only relative. You won’t be able or willing to make big leaps, but of course there is saving potential at E8/E9 (TVöD) if living costs are low and one is thrifty.

However, you won’t get far with 180000 - a simplistic calculation in this thread shows it quite well.

Well, let’s say the forum is rather cautiously optimistic and if you don’t pay for a house out of petty cash, you will first get torn apart in the air.

I think you don’t know the forum well enough: that’s definitely not true. Nobody here has to have petty cash (big or small) to be able to build.
However, we are not characterized by schadenfreude to rejoice over the ruin of some who miscalculated.

I think you don't know the forum well enough: that is definitely not true.

That certainly doesn't take 3 years.

However, we are not driven by schadenfreude to take pleasure in the ruin of some who have miscalculated.

It's always a balancing act. Just as unfortunate for all those whose dreams were taken from them too early.