Shell basement/foundation has stood for 10 years

Hello everyone,

we are interested in a very beautiful plot on a slope. A large villa was started there 10 years ago. However, the builder did not adhere strictly to the development plan, which led to a stop in construction. The defects were all basically approved later by a supplementary application. So there is a legally approved status. According to the building authority, I now have to check whether what is built exactly corresponds to the second supplementary application.
-How do I best do that?

Furthermore: on one side, a partial basement was constructed; on the other side, a foundation was built up and compacted with gravel, but this part of the floor slab has not yet been poured. Overall, water may have penetrated there for 10 years, even though it is now covered with tarps. In the basement itself, some walls also show moisture that apparently comes from above. According to our architect, this is not a problem. However, I would like to hear other opinions on the matter. Apparently, it was well built. The best bricks were used at the time, T8 (thermally insulated), which would still be used today and have living space quality. Furthermore, for example, you can see the second sealing membrane on the first brick. That caught my eye as a layperson. The exterior plaster is somewhat damaged and will certainly need to be renewed. Two full floors plus an expanded attic were planned. We want to put a bungalow on top of it. Statics would not be a problem, which I also assume from the original planning.

Opinions? Ideas?

Thanks!
Regards

I did some further research: .
The perlite-filled T8 retains its insulating properties even under prolonged moisture.
According to the product declaration according to ISO 14025. That's already good!

Are you sure that it is filled with perlite? With mineral wool, you would have a serious problem. The masonry will be saturated with water even without mineral wool. I would ask a professional.

Good morning!
Relatively certain.
At least where window sills are missing, I could look at the stones.
But I can also gladly chip off one or two stones from the inside and see what falls out. I think that is a good idea to be sure!
I am attaching a few pictures again for assessment.
Demolition is out of the question because the price would be too high. The location makes the difference.
South and north forest, sunny location all day, west with kilometer-long distant view.
The basement probably already cost 100,000 euros 10 years ago (the foundation seemed very elaborate.... unbelievably much concrete used).
Our architect estimates the current new price at 150,000 euros.

Picture 0007 is a picture of the stairs to the ground floor. Above it, the wood is sheathing, above that today there is a tarp. Just for orientation. Add a few more pictures.
As mentioned, two assessments are important to me:
-how do I ensure legal compliance SHOULD (building application) = IS (as it stands and lies) and that no sustainable damage has occurred due to moisture, so that I can build on it without concerns. Initial assessment preferably here or tips on what I should pay attention to and possibly which expert (structural engineer, building surveyor, etc.) would be appropriate here?!
I will not buy it without an expert opinion and the owners have no problem with that. It was even a suggestion from them.

Thank you very much in advance!
PS: If I take the land value (comparison new development area near us and disregard deduction for oversize and slope, slope is justified and I like the oversize) I pay about 35,000 euros for the basement. Feels not too much if I can use it.

The defects were all virtually accepted later by supplementary application.

The building permit from back then has meanwhile lost its validity. You have to apply for everything anew. For me, besides involving an expert, that would be the main point for a purchase.