I did some research on this some time ago for a friend and found out that the whole rent to own can be a huge scam.
The problem is that the person renting the home to own doesn't put away as much money for you as you think they are and they use scare tactics of...if you don't do this you will never save enough for a down payment. But, when the term of the lease is up, they don't have that much money put away to begin with. The information I found also indicated that these guys prey on people with bad credit.
It CAN work in theory but, the article indicated that you really need an attourney to look over the contract before you sign to make sure that it is equally beneficial to both of you.
Also, the homes I looked at with my friends that were rent to own were not even clean by any standard and were being sold 'as is'. And the paint was bad...usually most of the flooring was bad. THey would try to discount things by saying how easy the fixes would be and all. I found it comical because the seller was showing that he doesn't respect his business, himself or you by showing a house in that condition.
I would Research, research, research and maybe contact a realtor in your area to help you understand how they work.