ml wrote:
so how do the pro's do it??

The steel structure of the sky scraper is one of the best grounds you
could have. It is effectively a Faraday shield around everything.

You ought to find out where the ground connections for the existing
lighting rods are and use that. If there are no lightning rods around
(shudder) find some structural steel close to your antenna, and bug
(clamp) on to it. I would also suggest following an electrical panel
ground around to see where its ground is. They too ought to be on
building steel.

Good Luck!

Jake Brodsky
Amateur Radio Station AB3A