Fire crews arrived at the building in the 3200 block of South Shields Avenue shortly after 1 a.m. and found one exterior wall had already collapsed, said District Chief Arriel Gray Jr. of the Chicago Fire Department.
The roof caved in, and fire personnel spent the next two hours fighting the blaze, he said.
The Fire Department identified the building as DiFoggio Plumbing. The cause of the fire was under investigation, Gray said.
Bridgeport resident Jim Yarus said he rents space in the building for his snow removal and power-washing business.
He had come out to the scene Tuesday morning in sandals and sweatpants to survey the damage after someone had banged on the front door of his house to tell him the building was burning.
"I've got two trucks in there. I'm dying to see if they're OK," he said. "Two trucks I use on a daily basis, that I need."
For a while, he leaned his forehead on his hands against a chain-link fence, facing away from the fire into a vacant lot across the street.
"I'm bankrupt," he said.