First of all I'll tell you what I want to do.
First make a system role. That is (User, mod, admin, etc).
And add an option to add roles and these are stored in a different user table.
In better words. I need to know how to structure the database (tables) to match a role.
I'd go with 4 tables (only important information for this purpose added to tables):
users -- id -- role_id roles -- id -- name privileges -- id -- name -- value privileges_to_roles -- privilege_id -- role_id