What can Owner A do if he owns a 3-story building on property zoned for a 20-story building?

Owner A can sell his air rights, which allows for the potential development of additional stories above the existing structure. Air rights refer to the ownership of the space above a property, which can be sold or leased to another party for the purpose of constructing a building or extending an existing one. In this case, since the property is zoned for a 20-story building, Owner A has the opportunity to monetize the unused vertical space that the zoning permits.

This choice is particularly advantageous because it enables Owner A to not only benefit financially from the development potential of his property but also allows another developer to take advantage of the air rights to construct their building in compliance with zoning regulations. It is a common practice in urban areas where land is scarce, and maximizing development potential is crucial.

While the other options presented may have their own merits within different contexts, they do not directly relate to the rights and opportunities associated with the excess vertical zoning that Owner A experiences. Altering the building's structure, renting out the basement, or subdividing the land does not effectively utilize the zoning potential for vertical development like selling air rights does.