We recently built this barn door out of reclaimed barn wood purchased from Trestlewood in Blackfoot, ID. The door was very easy to build. We used an MDF core in efforts to keep the door from warping. We built it on a large flat concrete surface. We didn't have a table large enough since this door is about 8' x 8' large. First we laid out the mdf, then using glue and 1" brad nails attached the barn wood as tightly as possible. Then let it sit for a day or two to let the glue dry before building the other side. The most difficult part of this project was carrying that huge, heavy door down a hill from the garage to the home and getting it hung on the hardware track. Now it just needs need some appliance handles or something to pull this door closed. Considering some of these:
http://www.directdoorhardware.com/Rusticware-RW730ORB.htm