Wall painting is a repetitive, draining and perilous process which makes it an ideal case for robotics. The painting had been automated in the locomotive industry but not yet for the construction industry. There is a solid need for an itinerant robot that can move to paint inner walls of residential buildings. In this paper, the theoretical proposal of an autonomous wall painting robot is defined consisting of an arm that scans the walls vertically and is fitted on a mobile robot base to give the adjacent feed motion to cover the painting range. The design objective is to fulfill the criteria of uncomplicatedness, low weight, low cost and fast painting time. Ultrasonic sensors are fitted on the arm and the mobile base to regulate the motion limits and move in the room area. A control system is planned to control the arm motion and plot the mobile base motion.