About interstate works contract

1) I am interior contractor in Bangalore. Earlier i am charge to client 15 % TAX ( 60% VAT & 40% S.Tax). in GST how and what amount i need to charge to my client.

2) i am doing the work various place of india earlier i am registered where i am execute the work , now how i raise the bill to my client.

for example. I am registered in Bangalore and  i am execute the work in Delhi. material also i am purchase in Delhi and some of material come outside from Delhi. now i need to take new registration in Delhi or i will get purchase in my Bangalore GST no. if no then what is procedure for correct billing.