The blaze tore through the Jewson builders’ yard in Moor Road, Hunslet, and destroyed the shop building as well as Â£1.4m in stock.
But general manager Phil Robinson said that despite the devastation, they would be back at work tomorrow.
He said the business, its vehicles and its 15 staff would be relocating to another Jewson site, in nearby Gibraltar Island Road, where they would carry on as best they could.
He said: “All the staff are going there tomorrow morning and it will be business as usual.”
Mr Robinson said the lost stock was not just in the yard - where piles of timber now lie in blackened heaps - but in the fully-stocked shop.
This included painting and decorating supplies, windows and plastic drainage ducting.
About 100 firefighters were battling the blaze at its height, with locals hearing explosions after it broke out at around 2am.
Mr Robinson said the fire was so big that aeroplanes on their way to and from Leeds Bradford Airport had to be diverted from the flight path which ran overhead.
"Witnesses are saying there were three separate fires," he said.
"The building is going to have to come down, by the looks of it.”
He said they would make the building safe when the firefighters had finished on the scene, "because we have got to protect the residents".
Fire investigation officers have been at the scene today as they try to determine the cause of the fire. Nearby residents reported hearing explosions and smelled gas as the flames took hold.
The fire also damaged a carriage at the nearby Middleton Railway, with the visitor attraction forced to close its doors today.