Hi Nitin
It's a bit difficult to answer without understanding the full requirement, however this is typical of a SAP CRM set-up
You could have one role only and manage entirely by authorisations, but I've not seen a scenario where the difference in functionality per user can be managed entirely like this. Authorisations is not designed for CRM in this way.
Typically functionality is divided up per Business Role / Navigation Bar and minor differences per user can then be controlled with authorisations.
On my current project we're implementing 12 Business Roles/Navigation Bar Combinations.
For each Business Role, they are assigned to a separate Position in the Org Structure.
So, you might have a scenario as below
Level 1 - Org Model
Level 2 - Org Unit 1
Level 3 - Position 1
Level 4 - Business Role 1
Level 5 - User 1
Level 5 - User 2
Level 4 - Business Role 2
Level 5 - User 3
Level 5 - User 4
Level 2 - Org Unit 2
Level 3 - Position 2
Level 4 - Business Role 3
Level 5 - User 5
Level 5 - User 6
Level 4 - Business Role 4
Level 5 - User 7
Level 5 - User 8
Regards
Arden