I have built them out of 1 X 2" welded wire that I picked up at a farm and ranch suppy, It comes in various height's, I always like the 12". I got the crimping tool and fasteners for about 40.00. You will want to cut in a door to your timer so you don't have to lower or take the cage down to access the timer.
I will say this I am in the process of purchasing a couple of Eliminator plates. Years ago 25+ we did not have the problem with hogs that we have today. We installed them to keep the coons & squirrels out. It was a thrill the first time a hog showed up, however, I have noticed that the corn hits the cage and drops down under the feeder. The hogs come in, eat the corn and eventually create a wallow. I of course have winch feeders, so I don't have a problem having feeders undermined or turned over, however I don't like the wallow. In an attempt to raise the standard bar I am going to try the eliminator plate and see if it makes any difference.
If you don't have hog issues 1 X 2" welded wire attached under the barrel lip is the way to go. I think I sold 2-3 of the cages to some buddies and paid for everything, still had lots of material left over.