Membership: Membership levels and monthly payment

I am setting up the membership plugin to run a 6 month course - each month a new page will be made available with content. I am a little confused if I am doing this right.

Do I create one level that renews every month and then set up under the rules which pages they get access to for each month

mode serial

period 30 days

or

Do I create six different levels - set each one to to

mode indefinite
period 30 days

So every 30 days they will gain access to a new level but still be able to see the levels above?

Please help save me from this confusion! Thanks