See how I made the rock float: www.youtube.com/watch?v=PY5JwxpUDsY
The idea of this build is to feature the reveal, which can be achieved by leaving a gap between two wall/roof and having light source from the inside.
This build is only for inspiration with no mean to be a survival structure
This build is completely done in creative mode, mostly to help me fly and spawn items. However, no mod is added