A legal battle over a rooftop garden has turned a Manhattan novelist’s happy Upper West Side life into a horror story.

Lita Lepie spent more than 30 years in her large one-bedroom pad on West 78th Street, with its “artisanal” plaster walls and ceilings, and skylight.

But the piece de resistance was the exclusive access to the rooftop deck and garden, which Lepie, 68, says she was granted by the four-unit co-op decades ago.

But last year, a new resident moved into the first-floor unit, bullied his way into being president of the board, and began a crusade to oust Lepie from her $1.5 million apartment, she alleges in a $14 million Manhattan Supreme Court suit.

But the building has fought back in court, claiming Lepie has installed heating and ventilation equipment along with a television satellite dish on the roof without permission.