In traditional houses in China, it is generally believed that the gutter should be on the left. This is because in traditional China architecture, the left side is considered as the "positive" surface and the right side is considered as the "negative" surface. Therefore, the purpose of digging gutter on the left side is to accept the spirit of the sun and keep the balance of geomantic omen in the house.
However, there may be different customs and beliefs in other regions or cultures. Therefore, whether to stay on the left or on the right needs to be determined according to local traditions and customs. If you are building or building doorways in a specific area, it is recommended to consult local professionals or people to understand their preferences and traditional customs.