What is the best technique to calculate Warehouse space required for finished goods?

It depends on the stock rotation & service level you are providing.Other factors which should be considered in case of manufacturing unit is raw material & its procuring lead time which will help you to calculate space required for RM storage.

knowing the production capacity to output raw materials into finish goods and turnaround of finish goods shipment to distributor/customer

it depend of the selling department. The less stock you have, the less cost you have