Figures from the Health and Safety executive show 180 formal warnings were issued to roofing contractors across the region in 2009.
Working practices were so bad on 148 of those sites that work was stopped immediately by the HSE.
Inspectors are worried by a growing trend for companies trying to save money by allowing employees to work on roofs without scaffolding or other safety equipment.
Neil Jamieson, a Principal Inspector for HSE in the North West, said: “We’re worried that some roofing and building companies in Greater Manchester are trying to cut down on costs and undercut each other by not using scaffolding and other safety equipment.
“Falls from height kill dozens of workers every year and seriously injure hundreds more. But the number of deaths will carry on rising if firms don’t accept they’re putting their workers in danger.
“We will continue to take action against companies that do not take the safety of their workers seriously, and will prosecute those that fail to provide the necessary scaffolding.
“It simply isn’t worth companies trying to cut costs if lives are going to be put at risk. And it will cost them time and money in the long run if we decide to take any kind of enforcement action.”