Permission Based Folders Within a Project

Brief example of our specific use case; we have an internal team and an external team. The internal team needs access to all takeoffs throughout the entirety of the project, from the budgeting stage, to the bidding stage, to changes throughout the project, and the final billing stage. Our external team would only require access to specific drawings to complete takeoffs on the final billable items. I would like to be able to create a "Billing folder" within the project and be able to provide access to specific users only.

Another powerful feature (at least for our company) would be the ability to provide access to a specific page or folder with "view only access" to prevent accidental changes to critical takeoff items.

Thanks!