Random idea, probably won't work but what if he could build apartments and allocate each plot floor to a specific individual? This could make inns a reality as you could assign someone to a floor for a specific period of time. For apartments, the build/destroy permit could be for 4blocks high and 16x16blocks or something.
How it could work
Instead of plots taking up every space on the Y-axis, apartments will allow the user to claim a portion of a plot's y-axis. For example, one apartment would be *** tall to ***tall. to claim that apartment a person does /plot apartment claim. Apartment heights can be set by the owner of the plot(the owner of the plot can touch individual apartments even though they're privately owned like a mayor and plots). With inns, a person could be able to store there stuff in an apartment for an allocated period of time.
Random idea, probably won't work, have any suggestions, leave em' below.