I will preface this answer by saying I am not an accountant or a tax attorney. With that being said, anything you bring in is technically considered income. I have run several small businesses and my understanding is that you are only required to claim income from someone who you receive more than $600 from in return for your services or products. More than likely you will take in more than $600 from your roommate, so I would say you will have to claim that income.
Again, I would consult a professional for a definitive answer, but I'm pretty sure you will have to claim that if you want to abide by the letter of the law.