This video by my friend, Jim Long, tells about using roses as edible flowers. He cautions to be aware of what has been used on the rose petals as the sprays can be harmful to people.
One exciting tip he offers is a basic premise of "if the rose has no fragrance, it also has no flavor". I like that because the essential oils are what give herbs and flowers the flavor and fragrance. That is not to say only use rose petals if they have flavor, as the eye appeal is also important in dining, but if you want to embellish the flavor then smell first!!