Unless the seller has a recent survey available, I would definitely want one. Are you buying a lot in an existing subdivision, or elsewhere? If not in a subdivision, have you checked for scrub jays, which are an endangered species found in that area? If the lot is within a scrub jay habitat area it will be both difficult and expensive to get permits to build. Another question is utilities -- are they available at the street, or will you have to pay to run electricity in from another area? Running electricity to your lot can potentially run $20,000 or more. And I haven't as yet mentioned the cost of a septic system and well for water if water/sewer lines are not available. When buying a vacant lot it may save you time and money if you do your homework up front.