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

Hello everyone,

we have been living in our own home, a terraced (middle) house, since summer 2014. Our problem is a marten. We have had the marten problem since the first winter after we moved in (2014). At first, we couldn’t identify it, just some scratching and scrabbling under the sloped ceiling in our daughter’s room and then nothing for a long, long time! Last fall (2015) a few times again, as if someone was about to scratch through the drywall and OSB, that’s when we first researched it and concluded that it must be a marten, and now it was back again yesterday.
When I read the reports on the internet, this uninvited guest causes a lot of damage and I don’t want to know what the insulation looks like by now and how many carcasses are decomposing there! All suggestions for deterring martens using "smells" that need to be regularly placed nearby will not work for us because the marten moves in an area under the tiles in the insulation that we cannot reach. We also do not have an attic; it is converted and houses the heat recovery system! Our neighbors do not have the problem (or do not notice it), but we are the only ones with dormers on the roof, and here I can imagine that this facilitates or even enables entry for the marten.
Isn’t a new house supposed to be built so that unwanted guests stay away??
What options do we have against our builder, who nonchalantly says that we first have to prove that there is a construction defect/damage for which he is responsible?
Who establishes this chain of evidence or can establish it for us?
Would legal expenses insurance and then a lawyer help, possibly?
I don’t have the necessary small change ready to quickly set up scaffolding and commission craftsmen to restore everything and secure it against renewed intrusion and/or to secure evidence.
I have also already spoken with building surveyors, they are not familiar with such problems either and refer to pest control/forestry office, but these creatures are under species protection and when one goes away, another comes. Besides, the pest controller also costs money, especially since the animal is not regularly there; it is a 5-unit complex with many possibilities for the marten to get on the roof, and that certainly makes it more expensive. Setting up traps, checking, questioning neighbors, God knows...
Help, help, what should I do, how should I proceed, something has to happen!!

Best regards Klaus

Thank you for the constructive response with the ultrasound, it's not so bad for a start, but basically, why is one always the idiot in the forum when asking a question that is not so easy to answer?

You are always the idiot you present and feel yourself to be - or not.

You just want to hear that the contractor should pay nicely - but you probably won't get that answer, instead you will have to spend money.

Annoying, no question, but that's how it is as a homeowner - otherwise you just have to remain a tenant . And the additional, complicated situation with the terraced house is not someone else's fault either, you chose it yourself.

If you knew where mice hang out and what they eat

The money shark says no more (what does the money shark actually do?). He is now offended and prefers to take care of his millions instead of being active here in the forum.

Oh, aha, so that's how it is! So if I made myself look like an idiot with my question, I sincerely apologize, I didn't know that only people who already know everything are allowed to ask questions here!

Does anyone have experience with a "new building" that a marten has moved into, if so, I would appreciate an exchange of experiences.
Does anyone have knowledge of the legal conditions, e.g. how a house must be built, or whether it has to be built at all in such a way that no uninvited guests move in, please without personal assessments, then I ask for information.

And of course hope dies last, the hope that grants a spark of right that leads to not having to pay for everything out of one's own pocket, and this hope is entitled to everyone, it would only be too stupid to hang up this hope and blindly stuff the money into the jaws of the next best one and later realize that one is a real idiot.

: ditto