The easiest way is to use Designer > 7.1 for defining the data-roles in a VDB. As I last heard, it is going to released in next day or two. may be you can try one of their milestone builds available right now. But you can also had edit the "vdb.xml" for providing the necessary xml content. See "Data Roles" chapter in the Reference Guide.
Can you attach the VDB, so that I can see what is the issue?
Resolved. The corrupted vdb arose because the archiving process was scoping the contents of the archive beneath a root level directory. Hence the deployer couldn't find the META-INF directory or subsequently the vdb.xml.
Looking forward to Teiid 7.1 Designer which hopefully means no more file editing by hand.