Sitting in a house facing south, what influence does it have on my home if my neighbor builds a tall building?

Stand at your front door and look out.

See if there are any big buildings or obstacles in front of you, and what Feng Shui calls "backstab" has happened. A neighbor's satellite antenna, a street telephone pole, a church steeple, or a long road facing your door-all these can form the so-called "stab in the back." If something that can be a "stab in the back" is pointing at your front door, then in order to resolve this harmful influence, you should hang a gossip mirror at the front door with the mirror mouth facing outwards.