Is paving a parking lot outside the building boundary allowed?

Just for understanding: In this case, he wouldn’t have any disadvantage because my roof would also directly border his garage and thus the existing setback areas would actually not be affected!?

You are not allowed to build anything in a setback area. If he adopts your setback area and the garage is already there, the garage would become illegal. And that is why, as a neighbor, I wouldn’t do anything that would allow someone, in case of doubt, to prove official acceptance of your exceeding of the boundary length.

I dare to assume that a side building line is not affected here at all, and therefore nothing can be regulated by a transfer of setback areas or the like. The distance to the street-side property boundary does not depend on the neighbor's consent, especially not on that of the side neighbor.

I will probably soon have to pray that the Lord may throw some brains from heaven – given how often something has been asked here recently without any context. Does no one realize on their own anymore that the community cannot look into their head? :-(

Please post a sketch. I just have the feeling that everyone here imagines something different about your situation ;)

I will probably soon have to pray that the Lord throws brains down from heaven – there have been so many brainless questions here lately. Doesn’t anyone realize anymore that the community can’t look into their head?
:-(

Your prayers have been answered! :)

I have used all my brainpower for the art in the attachment and hope that it is clearer now? ;)

die Kunst im Anhang

... does not at least reveal any approval obstacle to me. I consider this roof to be included in the floor area ratio as if it were a paving. Since it covers such to the same extent, nothing comes on top. The exceeding of the length of 9m at the neighbor boundary is probably exemptable.

When it comes to grass pavers, caution is advised... according to our development plan, these are also considered sealed surfaces...

Here with us (postal code 045xx/Saxony) as well. It was also explained why: most homeowners would soon or in the medium term fill the grass pavers with the "filler stones," therefore the area is considered sealed.