Creating recipes of your own is not too difficult. Many brewers start with one of our Brewing Recipes or use a recipe from any of the many brewing books that we stock. From here, making the jump to formulating recipes of your own is not far. Really, it's just grains and/or malt extract, hops and yeast.
As long as you combine those things, you'll get beer. Whether or not it adheres to a particular style guideline is up to you. Many books even have a section that tells you which ingredients are preferred for each individual style. Get creative!