First, determine if the bird is a diurnal hawk (active during the day) or a nocturnal owl (active at night).
If it is a diurnal bird:
If possible, go up on the roof and completely cover any skylights with an opaque cloth to block the light. Turn off any lights, keep people away from the area and open the largest door close to where the bird is. The bird may take the hint and fly right out toward the light source.
If the bird flies into the warehouse toward dusk it may be perfectly content to simply roost in your building overnight. In this case, turn off the lights, close the doors and go home. Come back early the next morning, preferably before dawn, keep all lights off, open the largest door closest to the bird and keep all people from the area. Position yourself out of sight but in a place where you can see the bird leave. This is most successful if you arrive early enough to have the door open as the sky lightens.
With a hummingbird trapped in a building, we have had success gathering a big bunch of flowers and placing them in a vase just outside the exit door.
If it is an owl:
Most owls spend the daylight hours secluded in a tree or other structure and do not fly until dark. At dusk, turn off all lights inside the building, open the largest door closest to the bird, remove all people from the area and be out of sight but in a position where you can see the bird leave. Most owls will not leave until it is quite dark, so your timing is critical. The bird may also be disoriented and not fly out immediately even when it is dark, so be prepared to give it some time.