This is a spirit house. Whenever you build a home or building in Thailand you have to put up a spirit house. It is believed that spirits live on the land that you are building on. Therefore, you have to build a spirit house to give the spirits as place to dwell. The spirit house must be in a prominent place and it must receive daily offerings. This seems to be an older custom dating before the diffusion of Buddhism. I believe it comes from earlier animistic beliefs and was incorporated into Thai Buddhism.