In support of @Hal_Al 's response, it also depends on your intent. If your reason for renting out the room is with the "intent" to make money, then it doesn't matter if you make a profit or not. It's reportable income on SCH E. In a situation where your state offers a "renter's credit", if the renter wants that credit for the money they pay you, then it's rental income. You don't have much of a choice in that scenario and must register as a landlord with your state, report the income, and provide your tenant with any paperwork they require in order for them to claim the credit.
I am familiar with this process in the state of Hawaii. That state does not "legally" allow a "cost sharing arrangement" if one of the persons sharing expenses is the owner of the property or has any level of ownership interest, direct or indirect in the property.
