Dynamically Modify Role Permissions And Also Generate The Appropriate Sitemap / Menus?

I'm doing some research on security and sitemaps in ASP.net and am unfortunately running short on time. I have not worked too much with ASP.net security so I'm not completely sure if I'm heading in the right direction.

Here is my problem:

I have a public website (i.e. on the internet) that will allow any user to sign up to. The website will be developed using ASP.net webforms. These users may create other users and assign these users different roles.

Different roles have different restrictions and the menu is displayed appropriately. For example, a user acting as an administrator can see all menu options. Whereas a limited user will only see some of these menu items.

There needs to be the ability for users on our end to modify what pages certain roles can access. For example, if Role1 can do task X, we would like to be able at some point modify Role1 to no longer do task X. This would be done using an application built in-house.

User types (roles) are to be saved in the database. User permissions (what pages each type can have access to) are also to be saved saved in the database.

Here is something I am thinking of doing:

Implement the authorization and authentication set up built in to ASP.net using the web.config fileUse Sitemaps to dynamically create menus/breadcrumbs from the database

I believe it is possible to do the second one using custom providers (please correct me if I'm wrong). But I am not entirely sure if it's possible to configure the web.config file dynamically.

I suppose this is really more of a yes/no answer but I would just like to make sure I'm not going in the wrong direction. I will be using VS2008 and .net 3.5 framework.