Withdrawal from the work contract (The shell construction simply does not start)

Did you receive a cancellation policy at the time of contract conclusion?

If not, then you still have this joker. Provided, of course, I'm not mistaken...

My assessment: Ask your lawyer.

Did you receive a cancellation policy when concluding the contract?

Isn't that only relevant for "contracts concluded outside business premises and distance contracts (aka online)"?

Yes, what do you expect from your civil engineer? Profound communication? Why didn’t you communicate with him beforehand and get an idea if it fits

Come on, now you really don’t want to understand. It’s not about a philosophical conversation, but about clear and understandable statements.
An "Oh, my order list is full, we’ll come as soon as we can. I’ll get in touch when it starts, but we will probably have a 2-week delay" is a good statement that the OP could live with. But using the beautiful sunshine as an excuse for the weather is unprofessional.
And what should really fit interpersonally? It’s a civil engineer! The price has to be right, the reputation has to be right, and that’s it.

Isn't that only relevant for "contracts concluded outside business premises and distance contracts (aka online)"?

Let's ask the OP where he signed the contract. Or was that written somewhere and I missed it?