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?
Thanks
Mark