Generally, rent to own favors the owner NOT the tenant - rarely does it work out well for the tenant
You will be expected to give a NON-refundable deposit, as well as paying rent over and above the usual rent - only that extra rent is applied to the purchase, and that extra rent is also non-refundable if you do not buy the home for ANY reason.
If you do not qualify for a loan now, you better make sure you will qualify at the end of the lease term or you risk losing money.
There are a number of other potential dangers lurking for the tenant.........the sale price is decided at the beginning of the lease - what if the market changes? what if the house doesn't appraise out? what if the owner stops making payments on the house?
My advice is to rent in the usual way until you can buy in the usual way - you will also then have a full selection of homes from which to choose ........work on whatever it is that is preventing you from buying now.
Rent to own is NOT the easy road to home ownership some think it may be.