I was just playing on the pve7 server on washington. The guy's name was "maggot eater" or something. He claimed to be an admin and said that it was against the rules to build a base inside of a permanent structure and linked to this site. Immediately i couldn't log in at this site to check. I was suspicious at first, however maggot proceded to destroy a few defense barricades and then quickly logged off. I picked up a few structures and got everything that i wanted so i'm not too upset. When I did check the rules I saw no mention of building bases inside pre-existing structures and saw that maggot eater was not listed among your staff. I also saw this post and so wanted to reply that I can confirm the problem with this player greifing and impersonating an admin.
Building in, on or attaching to permanent structures or restricting/blocking access to any public area or spawn is prohibited on the PvE servers. Maggot Eater's name here on the forums is solomon2338. He is a moderator. If you see blue, orange or dark blue in the in-game chat, pay attention to the messages.
building in preexisting buildings means that your blocking other people's access to items the spawn normally and is a bit unfair so it's kinda against the rules but there is no punishment for building in preexisting structures apart from staff members blowing it up.