There is a balcony directly above my bedroom. I want to get some soil or sand on it and plant some plants. Does this affect Feng Shui?

Don't move too much. Pay attention to waterproof structure. It is ok to grow some plants in flowerpots. Also, notice that some people like to plant foliage plants or orchids, so they use black nets to shade the sun. This is not recommended, it will form a tight encirclement. Yeah, bad luck.

Now there are many balconies on the top floor, and perennial grass will be planted with flower trays to shade the sun and reduce direct sunlight. These disks are only a few centimeters thick, which is a very good consideration.