Flavoring buttercream is not hard to do; all it takes is a bit of patience, a good extract, and a great buttercream. Place the buttercream into a bowl and add the extract a bit at a time and taste as you go along to find your right formula. Where I work we add 1 ounce flavor to 3 pounds buttercream.  Once you find that perfect combination, always remember to write it down so you have it for next time!