Convert existing home into income property?

I have a 3 bedroom home in far North Dallas with an attached 2 car garage. It's about 350 sq feet and thought about converting my garage into income property. I have plenty of parking and where my garage is positioned I can easily convert it to where myself and the tenant could live quite separately. I really want to make extra cash to pay off my house. Do you think it would be worth it? I figure the cost would be about $15-$20k up front to build it. My mortgage currently is $1600 and hope to rent it out for at least $1000 a month.