Hi Dhanabalan,
Custom rôles can be made at:
Settings>Site administration>Users>Permissions>Define Rôles
Choose the rôle you want to edit, and then click its 'edit' icon, in the Edit column.
In the next window that comes up, click each tick box to Allow (or not), each capability for the rôle.
Good luck.
PS If you're going to be programming Moodle, I recommend Alex Büchner's book: Moodle 2 Administration. (See Chapter 6.) Rôles can be varied per user according to the place they are in in Moodle.