All South Korean roofs are curved at the ends giving the appearance of a smile. Traditional Korean roof construction has traditionally used many kinds of natural materials. They are made of neowa (shingle), giwa (tiles), byeotjib (rice Straw), stone giwa (tiles), eoksae (eulalia) and goolpy (oak bark).

Source: https://en.wikipedia.org/wiki/Traditional_Korean_roof_construction, https://www.factretriever.com/south-korea-facts