Which task is worthwhile to do yourself?

Often there is no time for that, ...

And exactly there lies the greatest potential for savings. If you take time into account from the start, you can save yourself a lot of money.

Yes, there are people who want to support the house project with their own knowledge as much as possible, but you don't have to.

And then you pay for that.

Sure, you can. But the screed layer will probably schedule you, then only have time in 8 weeks. And thus the house construction will be extended significantly, since it doesn't only affect the screed layer, but others as well.

Why should he? I set the deadline for example to be finished by 07/01, so the work should be done by then even if it means some "overtime."

I don't consider this discussion beneficial for the OP anymore – it's about EL, about slightly lowering the construction sum. And that doesn't work with small things like chasing or the time-consuming task of filling and painting.

It does work, but not to the extent most imagine. I think you can take the hours needed by the painter, subtract 10% for your own tools/somewhat more expensive materials (if you buy paint at the hardware store, that's your own fault), and that gives you the approximate savings in the low four-digit range. It's not a lot compared to the total sum, but every little bit helps and you might already afford the terrace boards that way.

Some feedback from the OP would be nice.

that means every builder, regardless of education, is capable of acquiring all the construction stuff in order to communicate with the craftsman on the same level?

and why should I, as the builder, have to communicate on the same technical level as the craftsman? He knows that best anyway and is paid for professional installation. I just need to know what I want.

Most architects don’t exactly shine with more than half-knowledge, and that only if you’re lucky.

Read, read, read

so if I were to become an architect, yes! but I don’t want to

For that, you pay the architect 200€ an hour. That is of course your good right, but nevertheless this topic contains the greatest potential for savings.

Sorry, but I have little understanding for such an attitude; if I’m putting up a hut for 500,000 or more, I want to know something about it and not just move in.
I’ll refrain from making a statement about "city people" now.

I see it exactly the same way, but it may be that outside the expensive south the GUs are cheaper, but they also have to calculate and make a living. The discussion for or against GU is a separate topic with many arguments on both sides. The statement was simply that there is a very high saving potential there. However, one must be willing to invest time and interest, as with craft work. Otherwise, it will go wrong. But where do you ever get something for free?

Nonsense

Not everyone has a technical understanding like you as an engineer.

How is a couch potato like me supposed to do individual awarding without help? You need someone from the field as assistance.

Otherwise, I would tender as follows:

1 front door + 10 windows ???

That's nonsense.
Before building our house, I had nothing to do with the subject either.
But you get plans etc. from the architect (or structural engineer, or thermal insulation certificate...) with which you can obtain offers.
Furthermore, you talk to the previous trade and then always know what matters. Additionally, you can also get advice from the building materials dealer and are then told what selection options there are.

My wife (physiotherapist!) understood the structural engineer's plans after a short introduction, so we were able to lay all the steel reinforcement ourselves, weave steel cages, etc.

There are countless tasks that are so simple that I would never pay anyone for them. And these are often tasks that the builder himself executes much more precisely and carefully with 100% certainty. Example: screed insulation, insulation between rafters.

Why should he? I say, for example, that I will be finished by 01.07, by then the work should be done, even if it means a few "overtime" hours.

You can forget about that in metropolitan areas, unless Stuttgart operates differently than the rest of the country. Four years ago, we contacted six companies for a complete heating system renewal. Three inspected the situation on site, only one submitted an offer. Schedule: "whenever it fits in." Room for negotiation: zero. In our rented apartment, there was a slight water ingress at the dormer (wallpaper damp in the corner). The landlord called a craftsman in March, someone came in June...

In our rental apartment there was a slight water ingress at the dormer (wallpaper damp in the corner). The landlord called a craftsman in March, someone came in June...

What do you expect? A 3-month lead time for this workload is extremely fast anyway. Therefore, you must also plan accordingly much lead time when requesting a quote.