Metal roof and it's effect on the antenna?
 

I realize that my metal roof necessitates the use of an external antenna, I was going to use one anyway, but I'm wondering how far above the roof would I have to place the antenna to minimize the roof's influence?
Thanks.
Bob

It depends.

UHF vs high-VHF vs low-VHF.
Antenna mounted on the close or the far side of the roof relative to the towers.

You haven't provided any data yet. A TVFool plot and a description of at you want to receive and where you'd like the antenna would be for starters.