Overview
This article covers the process for you to be able to include a class for members and their respective membership levels while still allowing for the public to register for it.
The Why
You may find your group wanting to offer classes and other offerings to both your members automatically while allowing non-members to sign up. This can be beneficial in many ways, and can allow you to charge the general public more for these classes, too.
How To Do It
In this case, you want to create a singular class that requires registration:

... and then in the Registration Billing section, you will set a price override of $0 for those that hold the certain membership(s) that you want it included with. It will require a registration by the members still, but it will be for no further cost.
It would look like this on the Registration Billing tab of the offering:

This setup will allow you to be able to have a singular roster and adhere to any enrollment limitations you wish to set.