Thermostat location in 3 story building
This is a common problem in NYC.  There's no perfect solution.
What I've done is put in an electronic thermostat with remote sensors on each floor.
Then, using the data I've collected, I tell the thermostat which devices to obey at each time interval.
In general, each floor is a degree or two off from the other ones, but the top floor can be much hotter/colder than the other ones, and, of course, you get tenants who leave windows open in winter...