Using roles, one can restrict access to your site. However, Drupal/Ubercart by itself can't restrict access to certain nodes (content pages) by itself. To restrict access to certain nodes you'd have to use the Drupal core Taxonomy module and a module like TAC lite or Taxonomy Access Control. Once Taxonomy is enabled, you can define a taxonomy on nodes that will be used to restrict access. With one of the contrib modules mentioned above, you can restrict access to this node taxonomy based on a role that you've created. With the role and taxonomy in place, the only thing that remains is to use the Ubercart Roles to start selling the role that you've created.