Before making any decisions, do check with your local building's department for any applicable permits; as for the lease portion of your question, do consult with an attorney who specializes in real estate, for all related documentation.
Unless you live in a community with CCRs restricting rentals...you should be able to rent our a room.
You will either want to study up on landlord/tenant law to the point where you feel comfortable or hire an attorney to help you. Make sure you have a lease that is legal in your area and that will cover the bases to keep you in control. Mistakes can be costly.