What phrase can I use instead of "pop the roof" to mean revitalizing, enhancing and expanding a building? I need to convey this idea without referencing a roof.
Gentrify speaks to revitalizing a building, with improvements that increase the value.
the process of renewal and rebuilding accompanying the influx of middle-class or affluent people into deteriorating areas that often displaces poorer residents
You don't specify the reason for the building work, but if the intention is to resell, you can use the colloquial term flipping.
House flipping has become a hobby or even business in several parts of the U.S. The goal of course is to sell the house for more than the cost of purchase plus cost of repairs, thereby earning yourself a profit.