Using PHP to hide a widget area with Membership

So I've been told that I can use PHP to work with Membership, and I want to hide the ads which are a widget in each area (and is the only widget in the area). What would be the correct code so that free members (as well as guests but I've set that up in the options already) will see the widget area, but the paid members (premium members) will not?

Nathan Pinno