Gst need to consider while new product costing

Dear Sir,

We are Antenna manufacturer & importing raw material from china with 18% GST . Also taking credit of GST.

While selling finished good Antenna charging 18% GST to customer. 

While make costing of our product we need to include GST value in costing or exclude from costing ? 

It is very confusing for me. Please advice.

Thanks 

Rahul