Storage rental can get to be the tail wagging the cat. Adding up the rental fees for one year will give you an idea, add it up for 5 or 10, then think how far that could have gone toward either purchase, or building, on your own.
Most storage rentals have lighting outlets of some kind, and if you'll look closely in the rental agreement you'll likely find a clause specifying something similar to "outlets supplied for lighting purposes only", although as already stated, some may be more lenient than others