There are better climbers on this forum than I who can answer questions on what types of rope would suffice but I can say that terminal velocity is, well, terminal. Unless you can get your drop height under 10 feet you might as well not bother. Much over 20 foot drop is the same as a 1000 foot drop. What you land on makes more of a difference than how far you fall if you are falling more than 20 feet. (now if you use one of those ball chairs instead of an office chair you might use that as a pad while jumping... <img src="images/graemlins/crazy.gif" alt="" /> Nah probably won't work.)