Marten in the sloping roof of the new building? Construction defect?

The fact is that it is quite difficult to get rid of the animals. Even if you catch them, trap them, and release them again, they are so cheeky as to come back.
Friends of mine had the same problem; the entire hut was turned upside down to find out how the marten got under the roof. In the end, sawdust was spread by the hunter to detect tracks. And lo and behold, it was found that the marten actually found a not completely fixed tile and thus gained access. The damage was not insignificant, but fortunately could be covered by insurance against animal bites.
Since these, although they cause damage, very interesting animals are subject to hunting protection, it is essential to seek professional help. The pest control operator can provide support but is helpless when it comes to putting a stop to it. The only one who can get this problem under control is the hunter with the appropriate proof.
I’m done....
Regards Sigi

I would first make sure that it is really a marten. We also had scratching, scraping, and rustling noises in the attic of our apartment. And the attic is small and there is absolutely nothing interesting up there.

In total, I caught 3 mice up there and released them a few hundred meters away in the forest. After that, there was quiet. Of course, you should really release them far enough away.

And the little ones were sometimes surprisingly loud!