I am currently writing a CMS and remember someone (it might have been on here) criticise the existing CMS for not having a robust enough user permissions system. I\'ve got a me
Have you researched existing solutions like RBAC? Whilst such a system would most likely be complete overkill for the particular nut you're trying to crack it would at least help to boost confidence that you're on the right track.
That aside, the general roles I'd expect would be along the lines of:
Administator - Total control of the system, can view logs (as you should be logging all changes), etc. plus...
Publisher - Can put content live plus...
Author - Can create content
However, how these roles are applied across the system is where things get tricky, as a specific user would presumably have different rights to different content areas/modules.