The emergency call came in shortly before 2 p.m. on Saturday, according to Deputy Chief Jon Morrison of the Casco Fire Department.
"A guy was in his barn trying to clean out snow. Snow from the roof was too heavy and collapsed on top of him," Morrison said.
The victim's family members said they came home from a day trip and found him pinned with his hand sticking out of the rubble, calling for help, fire officials said. They said it took rescuers 45 minutes to get the victim out from under the snow.
"It took three towns and probably 40 people just to dig out the snow. We had to use airbags to lift the roof off of him and we extricated him and he was Lifeflighted," Morrison said.
Firefighters said the man could have been trapped under the barn roof for more than an hour and that he had multiple serious injuries and was being treated for hypothermia.
Morrison said the incident served as a stark reminder to keep roofs free of heavy snow as winter continues in Maine.
"It's very important to keep your roof shoveled in this case and [at this] point, this is what happens when you don't. Too much weight on an older structure and it just collapses," he said.
The victim's name was not immediately released.