Paramedics treated the casualty after he fell from the unit on Granby Industrial Estate in Avon Close, Weymouth, just after 12:00 BST.
He has been taken to Dorset County Hospital but the extent of his injuries are not yet known, Dorset Police said.
Police and the ambulance service attended the incident. The Health and Safety Executive has been notified.
A man has been taken to hospital after falling through a roof at an industrial estate in Dorset.