Thank you for using Sitefinity.
Provided you have configured your custom role provider in Sitefinity then you should have UI access to the roles just as you would for the default role provider.
If you haven't then you can find some useful information on doing so in this post.
The process has not changed and it is akin to adding a custom role provider in any ASP.NET application.
If you do, then you can go to Pages > [Page] > Permissions. If you want it per page then break inheritance and select the appropriate roles who can view the page.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items