The document that you describe does not quite meet all of the requirements of a written lease because it does not set out the term of the lease (i.e. six months, one year, etc.).  However, it is evidence of an oral lease agreement -- which would be what is called a "month-to-month" lease agreement.  This means that either party can terminate the agreement with 30 days notice to the other (basicly one month's notice).  Since it is a month-to-month, he cannot come after you later for subsequent rent obligations.  All that he can charge you for is the time that you have actually resided there.  If you give less than 30 days notice, he could only potentially try to charge you for that last thirty days required to end the lease.  If he will sign a paper that acknowledges he has received your notice to end the lease and he has inspected the room and finds it in good repair-- then that would be helpful to prevent him from trying to make a later claim for damages against you.  However, the main thing is that you give him written notice that you are leaving.  If he refuses to sign an acknowledgement document, take good pictures of the room as you left it so that you can defend an action should he try to pull something shady later on.