New Delhi, March 17 -- A proposed megadeal in the self-storage business would create a $57 billion company overseeing square footage, if it were combined in a single location, of a small city such as Cupertino, California, or Chapel Hill, North Carolina.

Public Storage said Monday that it will buy National Storage Affiliates in an all-stock deal worth about $10.5 billion, creating a company with 327 million square feet of storage at nearly 4,600 locations in the U.S.

Public Storage said it wants to expand its presence in areas like the Sun Belt and other regions that are likely to grow in population.

The deal, if approved, would combine the largest and the fourth-largest U.S. self-storage companies by market capitalization. Extra Space...