thanks for your response.
There is no certain criteria, all the roles are created and associated to a single project manually. It would be very nice to create a role for each project automatically but not really necessary.
The most important thing would be, that the administrator can create a role which has only the rights to 1. Log-In, 2. See the Projects Tab 3. See his single Project and the Subpages and can edit them. It is especially important that he/she can’t see other projects or pages etc.
The link is associated to a “Edit Page” Link which is shown to me on this page as you can see here.