The incident took place in Dhobhar Kheda village late last night.
Police said 45 guests were on the terrace of the old single-storey structure to witness wedding rituals.
"When the rituals were going on, some guests started celebratory firing. This triggered panic on the terrace, and the roof started collapsing," superintendent of police (rural) Surendra Pratap Singh said.
He added that the injured were taken to the Dahagawa community health centre.
Two of the seriously injured were referred to Bareilly for treatment. Police said the organisers did not mention the occurance of the illegal firing.