If you’re thinking about Zigbee devices I’'d suggest to take a look here:
You might probably still set up one RPi per floor, but you wouldn’t need to run hass.io on each of them - Zigbee2MQTT would connect to your MQTT gateway (on your main Pi?!) directly so you don’t have to set up a whole ‘Master/Slave’ on hass.io via MQTT.
Drawback:
The number of devices per Zigbee2MQTT-dongle is limited (to 20, I think).