You should model the number of units for which you could receive market rent. Non-revenue units are usually:
• Down or off-line units that cannot be rented without significant capital expense (new kitchen, windows, e.g.)
• Rent-free unit for the employee (if an employee pays under market for the unit, then the delta should be in your Personnel OpEx
• Unit converted for amenity, model, office, storage, or other use
Sometimes you should return a model unit to the rental pool if:
• More than one model of that floorplan or configuration (you may not need a model for every 1/1 unit you have)
• Market does not require fully furnished model (you can partially furnish a vacant unit)
• Your model can double as an Airbnb/STR unit (although this really should go in other income)
• Demand is high enough to justify the removal of a model