Construction delay - What rights do you have?

But I am not the one who ordered the taxi, I am only the one being driven. The taxi was ordered by the travel agency since they ordered it at this specific time based on many years of experience with the departure time. So I don't even know the taxi driver and if I am now standing on the street and the taxi doesn't come, I can't order a new one within a few minutes.

Basically, I can't cancel a scaffold that has already been erected...

Sure, we are still on schedule but it was calculated: build, then about 3 weeks for the ceiling and upper floor, then it already takes 5 weeks until the windows arrive, during which time the roof structure and roof are covered, and then 2 weeks are planned for the exterior plaster. That makes 10 weeks in total. Of course, we have a buffer in the budget so that it can also stand for 15 weeks, but we can also start something else meaningful with the money instead of throwing it away senselessly...

Great, and respect that you do so much yourself.

From the information available I gather:
1. A prerequisite for the start of the stair and ceiling work was generally the scaffolding to be provided by the construction side.
2. On the agreed date, props were missing that would have been necessary for the work to be carried out.
3. At the alternative date, these props were still not there.
4. The props were supposed to be set up by the construction side (assumption) and could not be procured in time (delivery difficulties).

If that is the case, there is no basis for you to make a claim against the company commissioned for the stair and ceiling construction. The rescheduling is not their responsibility. They also have to figure out how to fit the postponement into their scheduling plan and will advocate for you so that it can happen quickly once the props are there. They don't have to hurry themselves – there is a long lever there that I would not try.
If that is the case, then you are obliged to pay for the scaffolding as long as it stands there. However, the scaffolding company can remove the scaffolding after the agreed time if they need it for another job.

As far as that is correct. But the company that organized the stairs and ceiling also commissioned the props. I started the shell construction in July and received the stone delivery. In my opinion, the props should have already been planned then. I finished the shell construction in mid-July and have been waiting for the props since then until August 7.

They were actually delivered on August 21. When I see the props—a square tube with head and base plate—no one can tell me that there were delivery difficulties. If I had known that, I would have quickly welded it myself.

And if someone tells me in August that it was vacation time... sure, but everyone knows the holiday schedule years in advance and we started with the foundation slab in May, so there was plenty of time to organize everything better...

In the normal case, one contacts the construction manager in such a situation. If one presents their concern here in a reasonable tone, it might be possible to negotiate a compromise. This could, for example, be a credit for half the amount of the damage. However, I would definitely not let it escalate, as then any basis for reasonable cooperation in the further construction process would be lacking.

We have made contact... I don’t want to cause any stress in between now since we still depend on the company....

There we kindly communicated that we find it unfortunate how everything has gone and that we are now paying for a scaffolding for nothing for 3 weeks.

We were basically told that they also depend on suppliers and that this is normal in the construction industry.

I wonder how it would work the other way around. According to the contract, I have to provide 2 helpers for ceiling installation and, as mentioned, the scaffolding. What if I had said one day before, there will be no scaffolding and everything would have to be ordered on and off? Then I would surely be at fault and have to bear the costs?

What I hadn’t really mentioned yet is that the steel supports for the carport were the reason for the first postponement from 8.8 to 19.8 because the site manager had poured the strip foundation for the carport too high! Therefore, a decision had first to be made about what we would do now, shorter supports or bringing the strip foundation to the correct height...
When this question arose, the boss was on vacation, so nothing happened for one week, from then on there were only 2 weeks left to shorten and galvanize the supports. We were promised to get it done by 8.8, but due to the heavy workload it was canceled at short notice and the 19.8 planned. We wouldn’t have had any major problems with that either....

But that this support for the window, which was not affected by changes, is coming only 4 weeks after it was actually supposed to come, is incomprehensible to us...

But there are repeatedly supply bottlenecks with steel. especially with 08/15 steel profiles. I am not surprised.

According to the contract, I have to provide 2 helpers for ceiling installation and, as mentioned, the scaffolding.

And what exactly does your contract say about the duties and deadlines for the company? Does it explicitly state that the company must have a support on the construction site simultaneously with the delivery of the masonry blocks or within x days after starting the masonry of the shell construction?