These days, the proposition that various applications in local indoor navigation have attracted significant attention recently is the provocative one. In order to improve and optimize the indoor navigation applications, we have to obtain the accurate floor plan of target place such as building and home environments. However, the belief that all the buildings provide us with accurate floor plan for indoor navigation is groundless. In this paper, we present a floor plan generator tool utilizing a smartphone integrated with an ultrasonic sensor gadget. In the measurement, the user completes a lap along the walls of all rooms. Then, the system estimates the accurate shape and size of the rooms. It leverages the inertial sensors, implemented in the smartphone, to track the user in the walking path. Moreover, the ultrasonic sensor in the gadget measures the distance between the path and walls. There are two main challenges to achieve optimized performance. The first challenge is that adjacent objects to, such as bookshelves, affect the accuracy in spatial layout estimation. To cope with this problem, we use a mixed Gaussian filter. The second challenge is that the narrow room, such as corridors, leads to the low accuracy. To alleviate this challenge, we implement two ultrasonic sensors in the reverse direction, and measure the distance between walls directly. The results from experimentations report improvement in shape and size estimation accuracy.