A 30×120 mini storage building will be able to give you around 3,600 sqft of interior space, which can be used to create 10 individual units at 36×10 in diameter.
Prefabricated buildings have the benefit of being quick to construct, an affordable price and resistant to many of the problems associated with wood such as rot, or insect infestation.
You could have your mini storage building fully built in under a few days, or even a few hours depending on your experience as well as the size of the kit.
Steel is a robust and reliable material which is weather resistant.