However, there is a hole in logic - what roof has any strategical advantage? Perhaps, one person will trip - rest of 99 out of 100, that are chasing you would eventually go through. Were there any further routes from the roof? Death from falling is my guess...
The reason why there would be higher step for roof, might have more something to do with dampness and to prevent wearing of that step, or to prevent leakage from the roof, that would stream down the stairs. SAeriously, who is making those stories, that makes no sense and who are so gullible to believe them? Are there any of those stairs seen on money? Drunks from my native town were telling stories about oak(which is recently planted - no more than 50 years), ythat they claimed were pictured on money... usually they wanted to claim that money after a story, if someone wanted to disprove it and brought their vallet out...