Class A buildings are generally considered to be premier in terms of the quality of construction, higher end finishes, state of the art building systems, and as a result achieve premium rental rates.  Class B buildings are more of the average and appeal to a wide range of tenants / users with rents that are average for the trade area. Typically these buildings have finishes that are in newer and good condition, buildings systems are in good working order and adequate, and they don’t compete with the Class A buildings.  Class C buildings are slightly below average in terms of the quality of finishes, typically older building systems, and appeal to users / tenants looking for simply functional space at below average rents.  We have more answers if you have more questions about commercial real estate.