Construction start still this year (November)?

I would have no concerns there. An open shell, where there is a draft, dries quickly even with a bit of frost. Drying a closed structure, into which hundreds of liters of water are introduced through interior plaster and screed, is much more difficult.

You can inquire what a proper winter construction site costs you. Read up on it and decide for yourself if it’s worth it.

I don’t want to judge whether it matters to the shell construction, but at least the workers shouldn’t lay bricks during frost. As soon as the adhesive mortar freezes, it no longer sticks properly.

Our building permit took forever to arrive (almost 4 months *puke*),

That's good! No reason to complain!!!

In the past, people used to leave the shell open through the winter because the dry winter air dries out the construction. If I understand correctly, you are doing masonry, right?
Then, as long as no frost is expected, you can definitely build up the shell. Construction stop only happens at the onset of winter, but by spring you are already a step ahead.

I will have the planned approach of the GU explained to me on Thursday. If it weren’t for all the (mostly older) unsolicited commenters from our surroundings, I probably wouldn’t be worried either. The GU will know what to do in case of frost outbreak. Everything will also be accompanied by an expert. And we might even be lucky and get the (flat) roof done in January. I don’t see the additional costs due to the winter construction site as critical (construction dryers, possibly electric heating for interior work). That will definitely be less than our extra rent for 5 months (from Nov-Mar) and the resulting standby interest + possibly higher costs for the start of construction in the new year. We are also not dependent on construction electricity; it comes from the neighbor and therefore has at least a normal tariff (and will be reimbursed by the GU up to a certain limit). Surely we will pay extra there, but we didn’t calculate so tightly after all.

That's good! No reason to complain!!!

In the past, people used to leave the shell construction open through the winter on purpose because the dry winter air dries out the building. If I understand correctly, you are building with bricks, right? In that case, as long as no frost is expected, you can definitely raise the shell construction. The construction stop is at the onset of winter, but by spring you will already be a step ahead.

That's true. But this only applies to a closed shell construction. If rain gets inside, the dry winter air won't help either :-p

So common for us: shell construction with roof but without windows.