Mr. F. Keep It Simple; A fridge kept well stocked with bottled water and / or other suitable drinks. Nothing else required, Jim

Be careful fitting fans in the roof space as, depending on the style of your warehouse roof, the warmest air will accumulate in these spaces and all you will be doing is blowing the warm air back down into your staffs working space. A previous employer I worked for saved tens of thousands in cooling costs by painting some of his warehouses white and simply cleaning the existing light coloured roofing sheets that had become dark and mossy.

Mr.Flibble - It's worth looking at having some roof vents if cost, security and pest control measures will allow. As per basic physics hot air rises, so allow it to escape rather than be trapped beneath roofs and gradually 'build down' into the warehouse space. The Victorians and Edwardians appreciated this phenomenon in their standard designs for school buildings which characteristically had ventilators, sometimes ones with ornate designs, along the ridges of pitched roofs. Over the years I've dealt with various complaints from schools about hot stuffy classrooms during the summer months. In addition to suggesting that schools with relatively modernn buildings restore roof vents which have become stuck with paint along their inside edges and/or through lack of lubcrication, I've added that external fire doors can be opened to allow extra ventilation unless local needs, e.g. security from unauthorised persons and/or retention of unruly pupils, would be compromised. Therefore, in addition to having roof vents at your warehouse, it might be worth opening external fire doors (if inward/outward security wouldn't be affected) in order to assist flows of air through the building.