Vinyl clad aluminum will dent, and careless use of ladders will cause problems. I have not had any problems with shielding from the aluminum, and run all sorts of radios in the house (ham, FM, Sirius satellite, AM, scanner, and my wireless TMobile Sidekick and other data and voice services) and have not found the aluminum siding to be a problem. The roof and glass windows are huge, electrically "transparent" apertures allowing all of the RF energy to pass through without problems.
Dark color like my chocolate brown are a problem though, and ultraviolet bleach>> I was told, when I called and asked Temna antennas, I think it was,