Symbolism, Imagery, Allegory
Roofs, for Lakshmi, represent prosperity. She and her mother have a thatched roof, which is made of closely bundled straw—it's cheap, and it leaks. Gita's father, who has more money than Lakshmi and her family do, has been able to put up a tin roof. For Lakshmi, a tin roof means that "when the rains come, the fire stays lit and the baby stays healthy" (1.ATinRoof.4)—both of which seem way better than their alternatives. And because of this, we understand that a roof symbolizes not just money, but warmth and health and general quality of life.
Of course, gold roofs are even better than tin roofs. When Lakshmi first sets out on her journey she asks Auntie Bimla if "all the roofs are covered in gold" in the city—surely the city must be full of people more fortunate than her (49.QuestionsandAnswers.6). And when they pass through the first city and there are no gold roofs, Lakshmi wonders when she will see them—and we see how naïve Lakshmi is.
After a long train journey with Uncle Husband, Lakshmi again looks for gold roofs as they come to their final destination. But all she sees is "roofs made of metal scraps […] roofs made of heavy paper […] roofs made of sheets […] but no roofs of gold" (61.ACityoftheDead.3-4). So what does this mean about both the prosperity of the people in the city and Lakshmi's expectations and dreams of possibility in the city? It's not looking good for our girl…