A 200 camera system is definitely a daunting undertaking.
Typically you'd need multiple recording servers organised geographically if there are multiple buildings. A recorder in each building to manage the cameras attached to it with a centralised server to manage them all, as a recorder can only handle a finite number of cameras.
An alternative is a server running Milestone software or a similar VMS, but the licensing price will be massive for a 200 camera system, particularly because Milestone licenses require an annual renewal fee.
You'll have to keep in mind the existing network, as 200 cameras are going to use a large amount of bandwidth. The standard resolution right now is 3MP but currently 4MP variants are superceding them, and these cameras use about 4-10Mbps each. The total quickly racks up.
Did you have any ideas in mind already?