It can be wire, but I'm going to let the hens decide. Afterall, most decisions are made by the hens in this world. I've heard good and bad about having them on wire. It couldn't make too much difference because they spend most of their time (when they aren't eating) in one of the nest boxes or looking out the domed window.
The REAL benefit of the slide out bottom is the ease of cleaning. I can just slide out a piece of masonite, swipe it with the 1' x 4' I cut off the full sheet and slide it back in - CAGE CLEAN in two minutes.
Now I'm working on lining the nest boxes with flexible PVC shower pan liner. $6 will do all six.