Building a good, reliable Zigbee network is dead simple. Just have a whole bunch of devices scattered around the area attached to your Zigbee network that can act as relays. The network will do the rest.
Here’s some products from my notes that should act as relays. This should give you an idea as to what you can use. In general, if it’s mains powered it will probably act as a relay, and if it is battery powered it probably won’t.
You might consider asking around for what products others use that can act as relays.