A 40×200 mini storage building will be able to provide you with approximately 8,000 sqft of interior space, which can give you 10 individual storage units with a diameter of 40×40.
Using prefabricated kits has the benefit of being quick to construct; this is because the separate parts are made elsewhere, then brought to your location for assembly.
Sometimes, you could have your kit fully built within a few days, or even a few hours depending on the size of the kit and your experience.
Steel is a reliable and robust material, which is inexpensive to build with and weather resistant.