According to some Rabonim a warehouse requires a mezuzah and a brachah is made. This would be true for a store as well and even for a shed (even one that you just keep bicycles and suckah panels and so forth) that is four amosby four amos (approximately 36 sq. ft.) I just spoke to Rabbi Chaim Schabes of New Hempstead and this is what he holds. I asked him if it mattered that the Rambam says a storehouse does not require a mezuzah and therefore if we put one up it should be without a brachah. He answered that since the Shulchan Aruch requires a mezuzah on a storehouse, we make a brachah when we put it up.