How to structure a seller financed purchase deal

[Philip L.]

I have the option to buy a house as follows 

Sale price $110,000
$40,000 Down
$70,000 loan

The seller says he is happy to fiance the $70,000 at 7% this is fine by me but what is the best way to structure this deal? or maybe the question is what are the options?
The seller has suggested a land contract as he would then have the house as collateral if we defaulted on the payments.

Any help with this would be highly appreciated