Those three pallets are sitting on 2"x6"x12' PT skids. I could have done 10 footers but the pallets would have hung over the edge a little. In hind sight, I would have not centered them on the 12 footers, I would have them go up to the edge on one end and built a little storage cubby on top of the protruding skids on the other end. Oh, well. Anywho, I attached them to the skids with angle brackets which are visible in the photo. I also did some extra bracing with some 2x4 lengths, which you can also see, under the pallets in between the skids. The bottom corners of the skids are cut off in case I ever need to move/drag the coop somewhere else someday (and it's a pretty good bet that will be the case).
Hope that helps! Feel free to ask more questions if you have them.
Katie