There are many pros and cons to owner carry finance and if it's for sale by owner.. Pro: little out of pocket for down payment if you can get someone/bank to come up with the 90%. You can take the upper hand if you can negotiate the price very low. Con: if he/she is an experienced owner then you could end up paying more for the land if you don't know what to do. Make sure you structure the loan correct: no balloon payment (unless you expect this) or balance pay off contingency before the set length.
E.g. I have seen Hmong people buying land for $500k and required to pay 50% up front with a contingency to pay in full within 1 year. They end up losing the deal and their money because they couldn't coming in with the rest of the money within the 12 months.
I suggest you talk to a broke to give you a CMA or check with your local court to see how much the tax assessor evaluate the land if there's not house.
Next get him/her to sign a purchase agreement on what you two agreed upon. dress a lawyer if you need legal help. Some lawyer will give free consultation the first time. (you can look online for a basic template.) Then take it to a title company and bring you funding.
Hope this helps.