The first question I would ask is:
Am I willing and able to take on the risk of a lease-purchase (rent to own)?
I know there are many reasons that people pursue these arrangements, but I have seen too many go down in flames to find them a winning choice for buyers. That's not to say that there aren't plenty of cases where everythig works out, but the risk ratio is always high on these arrangements.
Shawday has some great points laid out for you. The risk of foreclosure is always there and guess what? If the owner gets foreclosed on, you've lost your home and your money. The bank isn't there to honor the arrangement you made with the seller. It's not uncommon for the seller to disappear either.
I don't want to scare you, but these are real things that have happened to real people - right here in San Antonio. Texas as a whole looks down upon these arrangements but they are not illegal.
Some things to note:
Typically with a lease-purchase your rent is basically a ballon payment loan. You pay each month just like a mortgage, but without title (ownership) of the property. At the end of a prescribed amount of time, usually shorter term than most home loans, the rest of the balance on the loan is due (what's called a balloon payment). Most lease-purchase agreements come at a high interest rate (last few I've seen were running at 10%), so while paying those monthly payments, you're usually not making much of a dent in the principal of the loan.
The theory is that whatever it is that prevents you from getting a loan and purchasing a home will be resolved in the term of the lease-purchase option - bad credit, cash, etc. If those problems aren't resolved and you're unable to mortgage the balance or pay it off, you wind up having paid some expensive rent and once again have no home to show for it.
Obviously I don't know the particulars of why you wish to pursue this path, but if you haven't already, perhaps speak with a loan officer to see just what your situation is. Depending on what your roadblocks to getting a loan are, some may be fixed easily and quickly so that you may perform a more tradtional purchase in a timeframe that suits you. If the roadblocks are major, you may want to ask yourself if you're truly prepared financially for home ownership.
If you any questions, feel free to ask.
Hope that helps!
Matt Stigliano, Realtor (r)