Our Land Contracts have a three year term. At that time the buyers can switch to a conventional loan or stay with us OR we can tell them to get a conventional loan and pay us off. Three years of good payments usually make a good impression on loan institutions. The contract may be renewed at the balance due for another three years.
Only one of our tenants/buyers switched to a conventional loan and that was after 9 years with us and because of problems she developed financially.
I've never done a rent to own contract, but I'd imagine you both agree on a purchase price at the start. All necessary improvements, taxes, utilities, etc. are paid for by you and deducted from the amount you will owe. If you decide not to buy, the payments belong to the owner, but you should get something back for necessary work you had done. Necessary being things like roof, furnace. . .
It is a great way for people to get a start in home ownership. That's one reason we've chosen to help our tenants this way. Besides, they've lived there and know everything -- good and bad -- about the property before buying.