Tonight, I finally asked the police what the recently erected house is for. They explained that the abode is necessary for a re-enactment that is a part of the Posada, the nine days before Christmas (which also represent the nine months Mary carried Jesus). People may sing and play various parts in the journey to the manger (including a lady riding a donkey). According to my source, the manger/nativity scene (nacimiento) will be located on another side of the Zocalo.
Wednesday, December 12th, is the Fiesta of the Virgen Guadalupe. Then, the Posadas begin on the 16th. Time is flying, and there is so much to see, including the start of a manger at Cafe Brujula.