A Great Neck building was reduced to rubble just minutes after the last worker walked out for the day Monday evening. Authorities say the roof of a washing machine repair shop on Water Mill lane collapsed at around 6:30 p.m. Crews used special cameras to make sure no one was trapped inside after the collapse.It is not yet known what caused the collapse, but the fire chief says a cracked roof beam was due to be repaired Tuesday. A man who works near the building also confirms the roof had been repaired before.