Intercepting property, who has to bear the costs?

To pick up the original question: If you don't agree, then set your L-bricks and eventually something will start to shift. Then it will be difficult to explain to the neighbor that they should have supported themselves and that it's their own fault now. Therefore, it is important to find a joint, solid solution right from the start. Since you have the greater benefit from the structure, you will also have to bear most of the costs. Maybe create plantable intermediate levels and slightly slope them to also grant the lower neighbor a fair amount of light.

That it is almost a miracle that people do not regularly drag each other before the judge under such circumstances