I used cedar left over from a bar my husband made in our kitchen. I didn't have to purchase any materials as I used his left over pieces.
I didn't like my ledges with the back board, and I wasn't too keen on making the key holes. Instead of 24 inches I made my shleves 1 ft. long. I also laid the spacers so that the distance between the top and bottom of the ledge was less than the plan called for. This allowed me to attach a wooden strip (7.5 x 1.5 cut from the cedar 1x4 that I ripped on the table saw) to the wall that the barn beam shelf slips onto and anchors the ledges instead of using the key hole hanger.