BCM only has two "roles", the database creator and all the other
(shared) users to whom the creator has granted access.
The shared users have full read-write permissions, with a couple
exceptions I know of. They can't do backup/restore and they can't
delete items from the Deleted Items folder.
If you want to give a user read-only access to some particular
information (e.g. the Business Contacts) you could give that user
read-only permission to the BCM database (using sql commands), and then
create an Excel spreadsheet or Access report that retrieves the contact
information directly from the database.