"There are thousands of rooms in summer, and all the poor in the world are happy" comes from a poem by Du Fu, a poet in the Tang Dynasty, whose hut was blown by the autumn wind. The meaning of this sentence is how to get thousands of spacious houses, generally sheltering the poor people in the world, making them smile, and the houses are stable in the face of wind and rain.
The poet's own hut was destroyed by the wind and rain, but he pushed himself and others and thought of "the poor in the world", showing his broad mind of caring about the sufferings of the people.