West Midlands Fire Service was called to Church Hill Street, Smethwick at 5.21pm on Monday to reports of a blaze.
The fire was described as 'out in the open' but affected the nearby Star Supermarket, and resulted in Church Hill Street being blocked off.
West Midlands Police also attended the scene to assist with closing the road.
A spokeswoman for West Midlands Fire Service said: “At 5.22pm on Monday, West Midlands Fire Service were called to reports of a fire on Church Hill Street, Smethwick.
"First crews were on the scene in under two minutes.
“Crews from Handsworth and Smethwick were met with a large fire which had spread to a nearby supermarket.
"Crews used breathing apparatus and hose reel jets to extinguish the fire, which was out within 10 minutes of arrival.
"Crews remained in the area monitoring for hotspots and brought in a hydraulic platform from Oldbury Fire Station for crews to safely expose the fire damaged roof.
“Unfortunately it appears that this fire was deliberately set.”