Ian Griffiths, from Oldbury, pleaded guilty at Birmingham Magistrates' Court.
The incident occurred in October 2009 when two employers, Craig Thomas, 35, and Paul Leggett, 28, were working on the roof of some industrial units in Small Heath.
Both men had been contracted to repair the roof by Mr Griffiths.
Mr Legget lost his balance on a crawling board and feel to the floor. He sustained a broken leg, ankle, wrist and nose.
Health and Safety Executive inspector Mike Ford said: "Mr Leggett was lucky to survive falling 26ft through the roof, landing on the concrete floor below. The equipment provided to these men and the system of work used was completely inadequate.
"The precautions taken to ensure their safety fell far short of what is acceptable."
Mr Griffiths was also ordered to pay £1,408 in costs.
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