To create shabby looking roses quite easily, I find this technique of simple strokes to create that desired look to cakes and confections to work out great!
For this tutorial you will need a paint brush and either gel colors mixed with vodka or some dusting colors. To make some simple painted shabby roses, start with a pale shade of desired color and make some swirls. Next use the more concentrated color and paint some simple C shape swirls. Next use a lighter shade of the desired greenery color and paint some leaves, then add some dimension with the darker shade of the green.
Here are some cookies using this technique.