Why are you looking at a Rent To Own? These can be very, very good, or very, very dangerous. Make sure you are involving an attorney to represent you, most real estate agents do not even know their way around these transactions.
If you are in a declining market, and you are agreeing now to buy in 1-2 years, what happens if the price drops below the agreed upon price?
Many renters today are finding that the homes they are in are being foreclosed upon, and they are being forced to move with little notice and never getting their deposits back. What would happen to your transaction if the current owner failed to pay his loan?