If you are in a business of flipping houses, then all aspects of the sale will be reported on form Schedule C, Profit or Loss From Business.  On a Schedule C, you will report the gross income as your sales price and the basis will be your cost. You add improvements to basis, and you do not depreciate anything. Ending inventory is his cost of any properties not sold yet. Not sure of your question "Some of these properties are later acquired in an installment sale but some kept on lease sometimes for years,  are you saying a buyer or your client acquired the properties in an installment sale (if sold on land contract, title usually doesn't change hands until paid in full).