Building public structures

is there an admin cheat or mod that allows me to create buildings that the public can use that ;
for creating an npc town…
1 cannot be destroyed on pvp
2 cannot be targeted or destroyed by npc or the purge
and for creating npc base for players to siege
1 can be destroyed by players
2 cannot be targeted by purge

currently installed mods are pipi and coin and trade.
its a private server for friends and dont want to pvp but still want to do a siege. I just dont want to build stuff for the players only to have it wiped by AI.