Done it, but only on the Post Office Tower (now BT Tower) over 35 years ago. Mind you, would not attempt anything like that now after nearly doing a "Roy Hudd's Aerial" on my old bosses roof last year. I must admit looking at that picture made my b*lls shrink and my knees go all wobbly. I really admire those chaps who work on the sky scraper steelwork and high level aerial installers and the chaps who errect those tall cranes.
As the saying goes "going down is OK it's the sudden stop at the end which is a killer";)
H-B