Applicablity of service tax

Sir,

     Our one client doing fabrication on fabric for his client & his client engaged in selling of garments after paying appropriate excise duty & Some of the material were export by his client. Now my client who is engaged in fabrication of fabric is liable to pay service tax or not? Whether any condition is there in availaing mega expemption? Whether he is required to take service tax registration or not? I am also confuse in report clause 4 of Form 3CD Whether the assessee is liable to pay indirect tax or not?

Please Reply as soon as possible.

Thanks in anticipation