This study considers warehouse sizing decisions in an integrated single vendor-single buyer production inventory system by incorporating new decision variables and constraints associated with warehouse size into the formulations. Two typical inventory control policies proposed in the literature (i.e., Identical Delivery Quantity and Deliver What is Produced) have been investigated with consideration of warehouse investment costs. The numerical study shows that Deliver What is Produced is less flexible than Identical Delivery Quantity, resulting in the conclusion that the latter would be preferable when considering warehouse investment costs.