Construction site shut down due to missing Safety and Health Coordinator

It is clear so far, but then I have to create and post plans, right?

Do what (almost) everyone does. Hire the craftsman and let him work. I was recently working professionally in a new development area (there were about 40-50 houses in that section). SiGeKo rate: 0% Just from practical experience...

So if I understood correctly, I don’t necessarily have to appoint a coordinator but I can do it myself? I was informed by BG Bau by letter that the SiGeKo is missing. And without proof I’m not allowed to continue building. So I have to take some action and can’t just say keep working. The basement builder says that’s our issue, and Wolfhaus doesn’t really seem to think they have to take care of it either. I find it’s not so easy as a layperson to know how to behave properly!

if the trades all work one after the other, you don't need a...
only if several trades are present at the same time

See Müllerin. Otherwise, one-liner to the BG that you are taking over the task.

if the trades all work one after the other, you don't need a...
only if several trades are present at the same time

There were probably at least 2 trades on site. Basement builder and electrician for the foundation
earth layer.

If I understood correctly - I must confess, I have never read about this in a single-family house before - you have such a coordinator as soon as you yourself are one, and the "proof" consists of sending the corresponding declaration to the bureaucracy. They probably wrote to you that you did not have one (and you think that is literally a fact) - but what they meant, translated into plain German, was: "You did not check yourself as the coordinator." That is, you were probably only under the fearful belief that the term concealed a person with an imperially sealed yodel diploma.