This has to my least favorite of all the ways you can finance a home. If there is a mortgage on the home you rent with an option to buy, what if the seller does not make the payments to the mortgage company? Where does your rent go and where does that leave you? Those are questions that can be answered in another blog post for another day.
This arrangement permits you to move into your home and live there as a “tenant” while you raise financing. Try for an arrangement that permits all, or at least some of the “rent” to be applied to the purchase price. Lock in a purchase price too, when you begin your tenancy.