Use a circle cutter for the petals, and do it pretty much like a fondant/gumpaste rose... only use gloves because the chocolate will let your fingerprints show. There is a type of glove that I've seen others talk about to use when working with chocolate, but I don't remember what it is right off-hand. HTH!
If you have other, more specific questions, feel free to ask, and i'll help as best I can. I've only made these once before, but found it's like using the other mediums.