I’d start by checking your Development Application/Occupancy Certificate issued by your council. Our Development Application approval issued with City of Sydney Council includes this language:
“The on-site car parking spaces, exclusive of designated visitor parking spaces, are not to be used by those other than an occupant of or person residing in the subject building and any tenant or registered proprieter of the development site or part thereof shall not enter into an agreement to lease, licence, or transfer ownership of such car parking spaces to those other than an occupant or resident of the subject building.”
i.e. by all means rent your car space to your neighbours but council don’t want your building turned into the next Wilson car park. Neither do your neighbours btw – brings a world of security hassles depending on how your car park integrates with the rest of the building.