You can also use the easy_roles gem. It is available on github. This gem provides a bitmask solution for your different user roles. You just must have one model, e.g User, this model gets an attribute "role". Just checkout the docs on github. Devise + easy_roles + CanCan is a very good setup, it is very convenient in my opinion. I use this quite often.
Link to github: https://github.com/platform45/easy_roles