This was mine, it's been sold. Just some suggestions... Floor should be as high as the cab roof, have a toe plate all around the floor so stuff doesn't roll off, have some sort of tray for calls, lights, etc., gun rack would be handy, padded rail if you are going to use it as a shooting rest.
I took a bunch of pictures of the rigs that were at a coyote calling contest in Graham a few years back, they are on photobucket. Click below for a slideshow of all of them. Look close at the detail and you will get some good ideas to build one yourself. Varmint Rig Slideshow