Update user role when previous role expires

Hi,

My scenario - A user pays for membership to a site via Paypal. The site offers a 12 week educational course giving the member access to 12 weekly course pages (1 page a week). I want to restrict access to upcoming weeks pages until that week arrives. So, week 1, the member get access to the 1st weeks page. week 2, page 2, and so on for the 12 week duration, finally giving them access to all 12 pages. Then the users access ends/role expires.

I'm thinking that giving a member a role at signup/payment which has a 7 day expiry. When that week ends they are issued with a second role allowing them access to the next page. This would give the member either 12 separate roles or a role with the additional permissions.

I'm going to use Ubercart or Commerce to take initial payment and apply the 1st role.

Does anyone have an idea of the best way to achieve this?

Thanks for any pointers