Six fire engines and 35 firefighters and officers were called to a fire at a block of flats under construction in Fulton Road in Wembley.
Part of the concrete roof was damaged by fire.
The Brigade was called at 1256 and the fire was under control at 1340. Fire crews from Wembley, Park Royal, Stanmore, Harrow and Willesden fire stations attended the scene.
The cause of the fire is under investigation.