Building XX had two stories. Pollock remarks on the "extraordinarily squat, highly curved vaults" of the first story. The second story was completely fallen when Pollock visited in 1980, but it was known that the building rested on a low platform about 1.50 m high, with battered walls and typical three-member molding at the upper edge. This platform has since been restored as part of a major restoration undertaken by the Mexican government in the early 1980s. Teobert Maler, who reported on the site in 1895, was told the third story had once supported a perforated roof comb.