I rent a room and pay for an extra parking space in my complex for them. In what category do I expense that?

RENT

There is not a rent deduction or credit on your Federal return.  If your state has anything for renters you will be prompted to enter your rent info when you complete your state return.  As far as I know, the states that have anything for rent are Arizona, California, Connecticut, Hawaii, Indiana, Iowa, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, New Jersey, New York, Rhode Island, Vermont, Washington DC, and Wisconsin.

It is an a deduction because it's an expense. If I didn't have the renter I wouldn't have the expense.

I'm not sure you quite understood the question but I did expense it on schedule E where renting a room or property goes. I expensed it under miscellaneous. 

Oh---you mean you are the landlord and you are renting out the parking space to your tenant.  That was not at all clear.  We get plenty of users who are the tenants who want to know how to deduct rent.