Legend Creator - System Materials tool in the Creators group of the Startup tool-set can help create legends for various system materials. Let's create a Ceiling Materials Legend with the tool in this post.
The legend options and those legend columns look as follows in this example.
The content of the Ceiling Materials Legend may look as follows.
If another Ceiling & Materials layout option is chosen as follows,
then new Ceiling Materials legend may look as follows.
Detailed help can be got by following the path Project Setup => Creators => Legend Creator - Family Symbols on Revit Project Organizer.