Vat exemption for sez units in andhra pradesh state

One of contractor has approached to supply of the materials to one unit which is under sez units. If we raise the invoice to the unit it is completely exempted from vat or not. We were purchase the materials what they required items from inter state and intra state. If we send the all materials are exempted from vat under the state of andhra pradesh. If it is exempted what are documents collected from them for claiming of exempted from commercial taxes department. please give you r reply as soon . It's very important to us.