Building inspection of illegal construction takes place

Everything about the basic situation has already been said, illegal construction remains illegal construction. It would probably need to be clarified whether it can be legalized retroactively. If necessary, the window must then be closed and possibly also the access from the house to the attic. Although the access to the attic is not so easily visible, the window is. But you should clarify all this before the purchase or have the seller clarify it!