What loan amount is realistic for house construction?

If you apply the best interest rates and the lowest repayment, then that is correct. But you don't get those. When I calculate a full 30-year tiger, you come to €300,000 with a monthly payment of 1,135. I simply assumed an annuity of 5% for you, that should also be the case so that you are done in 30 years. Then it ends at €250,000.

Well, I have to agree with you there regarding the lending value.

The entire project will not be financed by any bank. My opinion...

I already wrote that the garage is included with the shell construction. Besides, I don’t understand how you come up with 50k for a garage. My father built a 9x6m masonry garage this year for 15k euros including the floor slab. Somehow I can’t shake the feeling that there are quite some regional differences…

I will never understand the prices asked for a masonry garage... We are currently building and also have a masonry double garage and it amounts to max. 20k and we are building right next to Munich...
However, I have to be clear about the rest, for me it’s not feasible.

Edit: Correcting with roof etc. 30k for garage

This is harakiri!
We built 160 sqm + double garage without a basement 2 years ago.
Also a lot done in self-performance (EVERYTHING DIY except roofer, screed, exterior plaster).
If you pay 220k for the closed shell, you will never manage with 80-100k for the rest.
There are still many smaller items that add up incredibly.
Window sills, interior doors, light sources (lamps etc.), suspending the ceiling on the upper floor (drywall etc.), interior stairs, stair railing, garage door, garage floor.... etc.
That quickly adds up to 30k, even if it is only material. Believe me!

Otherwise:
Walls/floors for 10k => textured wallpaper and DIY store laminate? Could work, but it's already tight.

Interior + exterior plaster for 30k: Can you really manage that completely yourself? Otherwise not possible.

What did you pay? Please provide a breakdown.

Thanks + regards
Michael

Together with my girlfriend, do you think the project is feasible?

more feasible. and again, she would be stupid to participate without property rights