Documents for the IT side of a Classified room?

Because we didn't have enough to do someone thinks we need to have a SCIF built and I am getting asked about technology costs. I've been reading a lot of acronyms from the .gov but I am not seeing a standard pointed out that we need to follow on the IT side. I was hoping it was a simple NIST set of policies. I've found plenty of room/building requirements.

I'm trying to understand if the network can share the same demarc connection or evidence needed to show they are separate, telephones, etc.