I took a piece of quality pine and cut the base for the platform, with nice rounded outside corners, then sanded it smooth. Then I took a 1/4 inch piece of hardboard and cut it as a back for attaching the platform and connecting it to the cage bars with bolts and washers and wing nuts. For now I've got it covered with a piece of puppy potty pad and taped on. This will not work for me long term, but will do for now.
Voila!

But you'll notice that Hoot and Annie are hanging out on the dowel below the societies' nest.

