Do you have any sensors to work with? You will need a way to find the walls to avoid, or open areas to drive towards.
If starting from scratch I would probably use an ultrasonic sensor like this:
http://www.maxbotix.com/ either 1 on a servo to sweep the area, or 2 pointed at the walls.
If the walls and floor are different colors, you might want to try a prior year's camera. However I think the software would be more complex.