I am aware of implementations like dynamic menu creation based on roles or pages inheriting from different base pages. Web.config for different site sections.
I do not want to use the default asp.net membership table structure in the database. I want to use something less complex.
I am looking at a possibility that roles can come and go anytime without affecting pages too much. I am also looking for performance.
You could create a custom RoleProvider, here is an article about it: http://davidhayden.com/blog/dave/archive/2007/10/17/CreateCustomRoleProviderASPNETRolePermissionsSecurity.aspx
Have it reference a many-to-many table that stores the role and user id relationships.
It looks like using a mature open source CMS framework like http://www.mojoportal.com/home.aspx or http://www.dotnetnuke.com/ is more suitable. They provide all the user and role management's UI for you already.
Otherwise you need to implement your own membershiprovider, roleprovider and lots of UI to handle your need.
It sounds like our product, MemberProtect, might be a fit for what you're seeking. It's primarily designed for online banking and similar sites that require quite granular control of role based access, but the principles apply equally to any type of site requiring RBAC.
You can download the lite version for free and it includes a sample Visual Studio 2010 project to show you how to help you get started and see some working examples of using basic roles & privileges within an ASP.NET website.
Jason