GST on work contact ( service + goods)

Sir I have entered into agreement before GST implementation to construct residential house in my plot, I have hired a construction company( architectural plan +materials+construction). Rate was fixed at 1500 ₹/sqft. But they don't have GSTIN till now. Agreement says that house will be delivered in ready to move condition ( completion certificate)

Can anybody clarify that do I have to pay GST to construction company also, because construction company already paid GST when they bought material from shop and the GST they paid on ship was already included in 1500₹/sqft, the money which I gave them.