Rent to own works great for the landlord/Seller but is a terrible idea for the renter/buyer. Until you qualify you are a tenant. You have no more rights, but the seller may try to avoid some of theirs and imply you have further obligations, but you don't. In most cases, you pay a fee to purchase the right to buy at a later date and that fee is to be applied to your down payment. You would then pay over market rent, with a portion being applied to the down payment. The problem is, if you find someone willing to do this at all (there are very few in most markets) they want an over market price for the house and will keep all of your additional money if you don't qualify for the purchase within the time frames.
You have a better option. Find the cheapest rental you can stand to live in. SAVE YOUR MONEY. Get on a strict budget and put every nickel you can into savings. Avoid indulgences and brew your own coffee, do your own nails and stay out of bars and restaurants unless someone else is buying. Some people will even get a second job and put that money into savings too. If you did this for a year, it would be a pain at times, but you would be far better off, have way more saved for a down payment and if you still didn't buy yet, you'd still have all the money.
The year will go by quicker than you think and you'll have put yourself into a much better financial position and will have many more homes to choose from when you are ready to buy.
Best of luck.