Edward Dean wandered onto the construction site at 100 Buckingham Road, Brighton, in the early hours of June 30 2008 following a night out with friends.
The 24-year-old tripped over an unprotected edge and fell 2.4 metres into a basement courtyard.
He was found dead at the site later in the morning.
Following a Health and Safety Executive investigation into the accident , PIB and two of the directors were prosecuted.
At Lewes Crown Court, the company, of 420 Falmer Road, Woodingdean, was found guilty of breaching health and safety regulations. It admitted it did not do enough to prevent accidents at work and was fined £30,000. It was also ordered to pay costs of £6,500.
Directors John Blankson, of 27 Glen Rise, Brighton, and Steven Moore, of Falmer Road, Woodingdean, both admitted to breaching regulations over construction site management.
Mr Moore was fined £30,000 and ordered to pay costs of £6,500, while Mr Blankson was told to pay £15,000 and costs of £3,465.