Rate content by the author's role I want a five-star content rating system, for example: 
if a premium user creates a content this will be rated with five starts, if a simple user creates a content this will be rated with three starts etc. I dont wont users to rate the conten.
Is something like this possible ???
I'll assume your using Drupal 7, you want to look into hook_node_update() this will allow you to run code whenever a node is saved/created.

From there you'll have full access to the node object in which you can use user_load() to grab the user object and check it's roles. Then you need to add logic based on the role to modify the nodes fivestar rating.