The owner of a Midtown office building spent $12.2 million on condo conversion plans before realizing the project was never viable because of an architect’s mistake, a lawsuit alleges.

The owners of 140 W. 57th St. relocated commercial tenants and went without renting space in its 14-story building — and then learned architects Goldstein, Hill & West allegedly missed zoning restrictions that limited the height of the Neo-Renaissance building and what could be done with the roof, the owner claims in a Manhattan Supreme Court lawsuit.

The architects were hired in 2015 to conduct a feasibility study. The owner is seeking $12.5 million in damages.