I have trapped hundreds of hogs over the past 9 years and here is what has worked for me. Your results may be different. I begin with 3 16' cow panels. Panels with 4" squares are best, but aren't mandatory. Over lap the panels a foot or so and wire them together well. I use electric fence wire. Once wired together, stand the panels up and move into a circle. I use a guillitine style drop gate set in steel chanel. The gate opening is 4'X4' and uses 4" square cow panel. I use several T posts in holding up the gate and securing the now round shaped trap. I also use a number of stakes to keep the panels from being lifted by large hogs. BTW, I make the trap sides 5' tall. Anything shorter will allow too many hogs to climb over.
I place an auto deer feeder in the center of the trap and feed plain old corn. Lock the gate open until you are seeing good hog sign inside the trap for a week or two, then set the trap and check the next day. In warm weather you need to check the trap everyday it is set. Hogs will die quickly in hot weather without alot of water. A water bottle really isn't sufficient as you have no idea how many hogs will be in the trap. The most I have caught at one time was over 20 (2 large sows and many midddle to small pigs) then I've caught a single very large boar before too. Trapping is fun, but your trap won't last long if you don't build it well. Build your trap to handle T rex and you will be okay. Also, trapped hogs are mean and nasty, so don't do anything dumb (like some of us) and decide to let some hogs go by lifting the drop gate while standing in front of the opening. In fact, never release a hog from the trap into the wild. You wil never trap that one agian, or many of his friends either. They are pretty smart animals...
There are some trap plans at texasboars.com
I bought both of my trap fronts there. Good luck..