In cities like Mumbai where it is tough to find new land at prime locations, redeveloping old societies is a way to create more residential or commercial spaces. Sometimes, though, the push for redevelopment comes from the fact that the building is so old that it can’t hold up any more.
Whatever be the reason for redevelopment, you have two options: hire a builder for a fee or a share of the new space or go the self-redevelopment route. According to an ET Wealth article, most redevelopment projects in Mumbai are set up so that the builder covers the redevelopment cost and in return, gets to sell some or all of the extra space once the redevelopment is over.