See if he has a title for it. If you can, see if you can take it to your inspection station to get a non-street title for you. That way, you have paperwork for it. Getting a vehicle as such can be troublesome for clearing your property rights to it.
Now, if you prefer, you can actually start on a tube framed street legal buggy once you get the frame/engine paper cleared. Many vw rails are street legal with only a plexy glass windshield (or eye goggles) and working/running lights. Check with your local DMV inspections for requirements.