Here's a you tube video that assembles a rosette. He uses an old turn table, but you can use a lazy susan from the kitchen:
http://www.youtube.com/watch?v=GOKQr07N5NY
As far as the pleated ribbon is concerned, just use the pleater attachment on your sewing machine (sometimes called a ruffler) If you don't have one, I'm sure someone in your guild has one, it's a pretty common accessory. Here's a pic in case you are not familiar with it:
http://www.singer-featherweight.com/...c_ruffler.html
They are adjustable, you you might need to experiment a bit with the settings to get a pleat spacing you like. I would then just use a large self covered button for the center. You could embroider something on the fabric first...