I was working with a big project recently and It has 5 sub domains along with root domain. In local environment I am complete with everything by making 5 folders inside main project folder. Initially I was not warn by client that we need to make all other 5 sites working as sub domain. My client said me that make other 5 sites in folder inside root domain and users will be same for all 6 sites including root domain. so User can login from any of the website and we need to maintain the same login to all other 5 sites.