Portable storage buildings are sold from dealer lots along the highway and delivered on a trailer; metal carports and buildings are sold by the same dealers or installed on site; a shed contractor builds one where a delivered building will not fit.
Short answer: The building itself is the easy part. What decides whether it can go where you want it is the lot: the zoning setbacks from the property lines, the septic tank and drain field it must stay off, and the size above which the county requires a building permit. A delivered portable building needs a level gravel or block base and a path for the delivery truck. Ask the county about the size limit before you buy, because a building a foot too big becomes a permit.
Reviewed by a manufactured home setup contractor and dealer.