Help: L/O or land contract offer, how to ask

I found a farm home for 199,000 I want to present a offer to either do a land contract or a lease option, my question is do I do this with the purchase price of 199,00 or do i go lower or higher? Also what intrest rate and terms should I use when I present this to the seller?How would you actuaully write this offer or would you make several otpions available to the seller, what would you write or say to them?