Been making these rose magnets on and off since last year:
The diameter of each rose is roughly the same as the diameter of a nickel. I didn’t see this in an instructional book, just started making these after playing around with polymer clay for a little while.
I used Premo! Sculpey and Studio by Sculpey polymer clay and powdered chalk pastel for some added petal color/shading. After the clay parts are baked and cooled down, I varnish the pieces in Future Acrylic Floor Polish (known as a superb polymer clay varnish, it doesn’t get sticky in humidity or over time), then glue on standard ceramic magnets which can be found at most craft or hardware stores with industrial-strength E6000 glue. I’m contemplating listing these on Etsy, though there are a few other sellers that offer similar items. Their roses look slightly different, though, so maybe I’ll just go for it. Perhaps I’ll make them in purple or do other flower types (e.g. lilies).
Each rose takes around 15 minutes on average for clay conditioning & sculpting time. I’ve made around 20 total, so that’s roughly 5 hours spent making these magnets so far!