A thick cut rock face with short rows. Very good fire protection. Materials themselves, do not rot or have problems with insects. A very natural, blend with nature look. Low maintenance with most applications.
Slate can be very heavy.
Adding extra support is sometimes required. Cost is greater than some other materials. Hard to walk on for a non-professional, without any breakage. The lifespan of the tile is greater than the lifespan of the underlayment. Hot is best for flat or semi-flat roofs that have good access and proper drainage.