Node Checkout and Role permissions

Hi,

I am new to Ubercart. I want to allow my site users to purchase certain roles. Once they purchase a role, they can post unlimited number of certain content types; but for those who prefer not to purchase any role, I want to make it possible for them to pay per post:

Users who already purchased 'Role A': Able to post unlimited number of content type A
General Users: Pay every time they want to post content type A

I am guessing that uc node checkout may let me do this but am not sure. Is there someone who has done this before or know anything about this task? Please let me know how to do this.

Thank you.

BB