This is my favorite way of making them http://cakesdecor.com/entries/466-cream-icing-rose-how-i-make-mine. I actually use the plastic bags that are used for produce at the grocery store. I am able to get the petals super thin this way and since I don’t have a veiner the plastic bag makes it look like the petals are veined. Here are a few I’ve done that way. 
