Thanks. Part of what I'm trying to do is figure out where to locate a
random wire on the roof of my building. It won't be my only antenna,
since I have a Wellbrook loop that I'm happy with. However, I like to
experiment with wire antennas and a wire would be a nice complement to
the loop.

The metal objects I'm primarily concerned with are ventilation pipes
that come up through the roof of the building. Any random wire up there
is going to get within at least four or five feet of at least one or
two of these pipes. I've done some trial experiments with 100 ft
lengths of wire, and didn't notice and detrimental effects of this, but
I'm always curious about what others have found.

Another concern is the paint that coats the surface of the roof. It's
the shiny aluminum paint that's used to keep buildings cool in the
summer. I don't know how much of an effect that can have. I lose a lot
of signal and gain a lot of noise if I let a length of wire drop down
directly onto the roof, but this is probably due more to the wiring and
appliances inside the building than the aluminum paint on the roof. The
noise of course drops way down when the wire is up 7 or 8 feet in the
air.