By now, you've reached the top of the office building. Congratulations! You're not on fire, but you will be if you don't find the stairs soon.
Look for the stairwell. It's probably the one with the sign that says 'STAIRS' on it. Or, at the very least, the one with the handrails that aren't made of actual fire.
Don't get too attached to your chair. It's not a comfortable place to stay when the fire alarm goes off.
As you head down the stairs, remember: the fire will not magically disappear if you just stand still.