I would tend to use Ethernet (the building may already have a local area network?) but WiFi or Zigbee may be possible
what communications facilities do the controllers have?
in theory, rs485 could work up to 32 devices in a 1000meters bus...that if you use a MAX485 as interface chip... but if you use the MAX487 ( or was 1487?) you could have up to 120 devices on the bus... ( of course you need to have all of them as max487...
also you can use/implement/buy a rs485 repeater...