Rahul,
Not only does the executing userid need the _SYS_REPO procedure execution privilege, the _SYS_REPO userid needs grant option for all actions on all schemas that are in the role which is being granted, for instance:
GRANT <privilege-list> ON SCHEMA <schema-name> to _SYS_REPO with GRANT OPTION;
Of course, if you are using hdbschema, etc. files to create your work products, they will already reside in _SYS_REPO's domain.