Ropes would burn in a fire. My suggestion would be to have heavy-duty chains which could be dropped from the roof or at intermediate elevations along the sides of the building. Someone could then utilize a clamp-like device which they could attach to the chain that would allow them to slide down at an acceptable speed. If this had been available at the WTC, those who had been trapped above the fires could have used chains on the non-fire side to reach floors down below.