The 91st richest man in the United States, a roofing company billionaire, died after falling through his garage's roof, local authorities said Friday.

Ken Hendricks, 66, was checking on construction of the roof at his home Thursday night when he fell through, Rock County Sheriff's Department commander Troy Knudson said. He suffered massive head injuries, according to his company, ABC Supply Co.

Hendricks was pronounced dead at an Illinois hospital early Friday morning, Winnebago County coroner Sue Fiduccia said. An autopsy is planned for Friday.

Hendricks was the founder, chairman and chief executive officer of his company, the self-described largest wholesale distributor of roofing in the U.S. The company does about $3 billion (euro2 billion) in business a year.

Hendricks had a net worth of $3.5 billion (euro2 billion) in September, according to Forbes magazine. That made him the 91st richest person in the U.S., according to the magazine's ranking of American billionaires.

But he seemed unfazed by his wealth.

"It doesn't make any difference to me; I can't spend it," Hendricks said in an interview with Inc.com in September 2006. "I'd have to sell the company, and I'll sell the company over my dead body."

Hendricks, the son of a roofer, worked side-by-side with his father growing up. A high school dropout, he started his own roofing business at age 21, according to his biography on ABC Supply's Web site.

Tired of having to deal with multiple suppliers scattered around the country, he and his wife, Diane, started a national supply distribution chain in 1982.

The company celebrated its 25th anniversary this year, with 6,000 employees in 390 locations nationwide.

"This is an enormous tragedy and a great loss to the family, associates and the community," ABC Supply said in a statement.

The couple had seven children, according to their biographies.