Hello! Im a player from Estonia, first of all I want to sorry for bad english.
I have an idea that might work.
Server owners/admins/moderators build a city (team blue side), build everything from apartments to shops etc..
After that the owner(s) needs to "bless" those houses, just typing /bless, if owner(s) has finished blessing that house, it's blocks are going to be indestratuble.
Also owner(s) cover the city with wall. Inside the wall where's city, there is killing forbidden, outside the wall/city is only killing. Also greens are not allowed to enter blue's city

Scripts brone.