Preston Crown Court fined the Ulverston-based firm Peter Mawson £200,000 for the corporate manslaughter offence, and £20,000 for safety breaches.
Peter Mawson, owner of the company, was sentenced to eight months in prison, suspended for two years.
Mawson was also ordered to carry out 200 hours unpaid work and publicly to advertise what happened on the company website and to take out a half page spread in the local newspaper.
Jason Pennington, 42, fell through a skylight onto a concrete floor 7.6m below in 2011.
Pennington was working at West Cumberland Farmers LTD, in Lindal, Ulverston.
The 42-year-old was taken to Furness General Hospital where he later died.
Chris Hatton, the investigating inspector at HSE, added: “Jason tragically lost his life because the company that employed him did nothing to make sure he was safe while he worked on a fragile roof.
“Peter Mawson knew the clear panels on the roof weren’t safe to walk on but neither he nor his company provided any equipment to prevent workers falling to their death.
“If scaffolding or netting had been fitted under the fragile panels, or covers had been fitted over them, then Jason would still be here today.”