Renting garage attached to 4-plex to non-tenant?

[Adam Juodis]

I was curious, could you rent out a garage that is attached to your rental property, to someone that isn't your tenant? I am interested in a 4-plex, and upon receiving the financial info, the owner was only able to rent out 1 of the garages to the tenants. If the tenants do not want to pay extra for the garage, could I potentially rent to renter next door that does not have enclosed parking? Any legalities that come with this? The garages do not have a entryway into the 4-plex.