So basically, in Chinese – in ancient Chinese architecture, the roofs are – each tile is curved – and the roof is built in a jagged way, so that it’s uneven. And the point of that is to keep the demons from sitting on your house, because if your roof is slanted or flat, the demon will be comfortable there.

My informant also told me that many roofs today are still built with curves and slants. Even people who are really impoverished and live in shanty houses, will build their roofs with several pieces of tin or wood to make sure that there is still a slant. My informant said that when her family moved into an apartment complex, her mother believed that the “place was fucked” (as my informant put it) and that misfortune would befall those who lived there because the roofs were all flat. Buddhists believed that curved roofs would ward off evil spirits believed to manifest as straight lines. So the ideas of traditional Chinese architecture have been passed down and people still hold deep beliefs concerning them.

more information can be found here: http://library.thinkquest.org/10098/china1.htm