In order for a Warehouse to be upgraded, a Temple must be built. The Warehouse's resources are used to train units, build buildings and buy technology upgrades. It is ideal for the most efficient bases to be equipped with six warehouses to boost available resources. Of course, the number of warehouses you can build is limited to the number of base pads you have available. The best combinations of warehouses are five to seven normal warehouses, or three blessed and two normal warehouses.