You are desperate!
Your Credit or Finances, or both, will not allow you to go the conventional route:
You need the Seller to help you out!
The Seller will know it, and you are going to pay dearly for this service:
There aren't too many altruistic Sellers out there.
The terms that can be written into a Lease/Option can be dangerous to you:
How long is the Option period?
How much money are you putting in to the Option?
What happens if you are not able to execute the Option?
How do you know what your financial situation will be 2-5 years from now?
How much is the rent in the meantime?
Who will be responsible for maintenance and repair in the meantime?
What will be the Market Value of the home in 2-5 years?
What will be the Selling price 2-5 years from now?