I've got to admit it—the role/roll homonym is a hard one for me. It's one of the ones that I know there are two different words with two different meanings, but in the heat of the moment of writing and revising, I always write "roll." Over time, I've learned that about myself and now I always check for that error, in my writing and in my clients' work.
Role: a part to play
Roll: to move forward by turning on the axis; a document that can be rolled up; a list of names
The way that I remember this is that role has ONE l and ONE definition: to play ONE part. Alternatively, roll is in SCROLL—a document that can be rolled up and that can be used to create a list of names.