How cities should work.
Owner buys city stone. Stone gives owner a plot of land X by X and is divided evenly into smaller plots of X by X. The owner may then add players to the city by granting them citizenship and one or more of those plots. The player may then build only in his/her plot within the city. Citizens may not take any materials that do not belong to them. However The owner of the city at any time may decide to remove materials from anywhere in his/her city and those materials go back to the owners inventory. If the owner of the city decided to revoke a players citizenship or the player decides not to be a citizen any longer all of the players materials are returned to him or her from the city.
I can see a plot system being handy