Any purchase of real property is complex. You need to structure the agreement to indicate the term, the amount of rent and the amount of each payment that will go towards the down payment on the house. Can the rent be raised? Wil the portion for down payment be raised,too. How can the buyer or seller get out? What happens if the buyer or seller dies? What penalties will there be? There are many more contingencies. If you wish, draw up a document. There are forms available--check FreeAdvice's forms to see if the one you need is available. It might be a very good idea to run the contract by a real estate attorney to be sure it fits your situation.