I heard it start raining and as I headed outside of my base to take a look, I saw the rain falling before I got to the door. This is not a case of looking through the blocks at the rain, but appears instead to be rain falling through my ceiling. It is very off and on and occurs on one side more frequently. There is a sweet berry farm above me that utilizes slabs and stairs, but it has a block width of dirt between it and my ceiling. The ceiling is made of solid blackstone and the home was carved into the side of a hill. Could possibly be replicated by experimenting with non-solid blocks on the surface with thin layers of solid blocks beneath.