Oops, typo: I should've typed "...so there's _no_ electrical conduction between shingle tabs." Sorry 'bout that. Sorry, Jerry, but I agree with HR--there's a BIG difference between a "real" metal roof (say, using corrugated steel) and a metal roof made of coated, non-conductive, steel shingles; with the former, it'd be worth it to tack weld bonding straps so you'd have a phenomenal counterpoise, but with the latter--bad idea, let alone impractical. However, a properly installed roof mount for a vertical is well worth it! 'DGJ: I'm surprised asbestos is still used anywhere--interesting! As for a counterpoise, nothing says that radials have to radiate away straight out like daisy petals for it to be effective--you can wind them any which way. True, the counterpoise would be more effective if it radiated outward like a daisy, but you're in a compromise situation, anyway, so just do what you can by laying down fair number of them that'll conform to the shape of the roof. (Don't ask me how many--that, I don't know. There's a practical minimum number of radials for a counterpoise to be effective, but I'm sure a wisened ham here can clue us in on that (for a compromised installation like yours.)) BTW: I used to live in Douglas, AZ, so I know your pain when it comes to heat out there.