Developer or General Contractor: Is the Real Estate Agent and Developer Regulation valid?

What disadvantages arise for us in the present situation, or is it even an advantage if the property already belongs to us from the beginning?

If the property belongs to you, you bear all burdens and risks. How is the sudden destruction regulated -- with regard to the work (=house)? In other words: What happens if a comet destroys the house the day before acceptance? Who then has the short end of the stick? Second question: Is there a fixed price for the completely finished house including all incidental construction costs?