The floor of your storage unit may matter depending on your circumstances and the amenities available at the storage facility.
If the storage unit is on the ground floor, it may be a drive up unit. That means you can drive your car or truck very close to the entrance of the unit to load items.
Another issue with units on a higher floor is that you may have to climb a flight of stairs to access the unit. Most facilities do have elevators, but they are not always operational, which could make transporting items to and from the unit more challenging.