The researchers studied different types of roofs for solar greenhouses in a mountainous area in Ningxia to see which one was best for saving energy and money. They compared the cost, temperature inside the greenhouse, and amount of light each roof type let in. They found that the greenhouse with a certain type of roof was the most economical choice because it had a lower construction cost, better insulation, and more light. This type of greenhouse was the best fit for the climate and economic conditions in the area, making it a good option for future construction projects.