Size is approx. 3" x 5" but designed in mm. It printed OK but I would scale it up in Simplify3D (or whatever you use) maybe 25% because the bird legs are on the thin side as is (but they are ok). My wife sure likes it. I printed in PLA using fine (.1mm) setting for the brackets and medium setting (.2mm) for the shelf itself. One file is for the shelf and the other is for one bracket - make two of those. Make sure you scale all pieces the same so that the holes line up. Use super glue to attach the brackets into the shelf holes. I used a raft and support for the brackets and neither for the shelf.  I designed it using Fusion 360 and Simplify 3D to slice it. It was printed on a Flashforge Creator Pro.