Firefighters were alerted to the fire at about 3am, where a passer by saw flames appearing on the roof of the Millenium Way store.
They used an aerial appliance to get onto the roof, and saw that a big plant, approximately one metre squared in size, was on fire on the staff's roof patio.
The crews extinguished the blaze with hose reels and two breathing apparatus and left the scene at about 4am.
Bracknell's watch manager Michael Fulwell said the blaze was caused by burning peat and soil after cigarettes had not been put out properly.
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