Hi Uday,
Well at present there is no built-in function to copy a role.
You can check the following threads, in one of them a SQL procedure is there regarding the same.
http://scn.sap.com/thread/3330552
http://scn.sap.com/thread/2064390
If you create a .hdbrole file in HANA Development Perspective, then you can extend that role
Regards,
Vivek