Billing in gst

Yes as far as project is completed he can bill the client with charging GST.

But works are not yet completed.He Made a bill as and when some part of work is completed.bill format is like

Constraction work          xxxx

20% claiming in this bill  xxx 

Igst                                   xx

That's what I am telling, partly completed work can be billed and GST can be charged thereon.

thank you sir