The incident took place on Tuesday evening in Old Ramesh Nagar locality when the girl, whose parents hail from West Bengal and work as daily wagers here, was alone at her house, Karnal Superintendent of Police Pankaj Nain said.
The accused identified as Sandeep, a drug addict, lured her to his home and sexually assaulted her, the SP said, adding that fearing she may narrate the incident to her parents, he threw her off the roof.
Later, she was found lying unconscious in a plot by her family who were searching her, he said.
The accused has been arrested and further probe is on into the matter, the SP said.