I built this box trap last Fall and started using it last month (January). It's 8' deep, 4' wide and 3' high. First catch was these four small ~60Lb shoats. It uses two swing doors in a saloon door configuration. The feeder set up over it keeps it baited when I'm not around. The frame is constructed from bed rails, I had to purchase the mesh panels and door hinges. Since this photo was taken I've added some additional T-posts at the corners to hold it in place.
One problem is that we've caught deer a few times in it, and they're a pain to release. They go nuts, jumping and bouncing around inside the trap. I'm going to rig up a cord that will allow me to pull the doors open while I'm standing outside the trap.