Subsequent construction of carports at a house on a slope

Is the sidewalk lowered? If not, is it even allowed to lower it at that spot for an access way?

a few 10,000s"

I don't think you will reach six figures, but a high five-figure amount should definitely be expected. We had an offer for 26m retaining wall with 180cm high angle stones and 14m retaining wall with 155 - 80cm stones, 50cbm earth excavation + disposal, just under 45k. Our costs now (with a company whose owner is a very good friend of our very good friend :) ) amount to around 20k + about 1.5k for earth excavation + disposal. However, he gave us the angle stones at cost price. So that's already a very good offer. Our experience was that it is very difficult to find companies for small and also difficult projects. Therefore, I think it might be a bigger challenge to find the right company.

How much space do you have from the parking spot to the house and what kind of height difference are we talking about here? The problem is not only that the finished structure has to hold, you also have to be able to secure it during the construction phase. This raises the question for me whether it is even possible to slope it off. Usually, a retaining wall is inclined against the slope, so you’ll need about a meter more space there than you think.

The sketch reminded me of a snapshot from vacation:

I would first check if you are allowed to build like that. Possibly the proximity to the street prohibits such parking spaces since you can only drive backwards onto the street and thus endanger the flowing traffic (or park backwards...). This is not allowed on federal roads, district roads would probably be okay (in NRW).

Currently, this was a problem with a family construction project. They had to create space (house also on a (steep) slope) to be able to park parallel to the street.

The building permit has not yet been granted - but there is a "good connection" to the building authority and the project was given the green light as an oral preliminary info.

Is the sidewalk lowered? If not, is it even allowed to be lowered at that spot for an access?

Yes, it is already lowered! In the old building permit for the house, parking spaces were already approved at that spot.

I don't think you will reach six figures, but a high five-figure amount should certainly be expected.

We had an offer for 26m retaining wall with 180cm high angle stones and 14m retaining wall with 155 - 80cm stones, 50cbm earth excavation + disposal, just under 45k. Our costs now (with a company whose owner is a very good friend of our very good friend :) ) amount to around 20k + about 1.5k for earth excavation + disposal. But he let us have the angle stones at purchase price. So already a very good offer.

Our experience was that it is very difficult to find companies for small and then also difficult projects.

Therefore, I think it might be an even bigger challenge to find the right company.

The slope at our place is probably significantly steeper, so it probably concerns considerably larger amounts of earth. But those are still valuable info, thanks for these experiences! I also have the fear that it will not be easy for us to find a civil engineering company for this project.

How much space do you have from the parking space to the house and what height difference are we talking about here? The problem is not only that the finished structure has to hold, you also have to be able to secure it during the construction phase. For me, the question arises whether it can be properly terraced at all. For this, a retaining wall is usually inclined against the slope so you will need about a meter more space than you might think.

The sketch reminded me of a snapshot from my vacation:

Space in front of the parking space should be about ~1.5-2m - hope that is enough for the terracing. The slope itself actually looks similar to the one in the photo. The height difference between the street level and the first house entrance level is about 5 m over a length of approximately 8 m (i.e. slope angle about 32 degrees).