Hello - I need to cut a "perfect" vent-stack hole in some metal roofing. Are there any suggestions as to the best method? Should I use a bi-metal hole saw? Electric metal shears? The roofing is a bi-ribbed design which leads to my next challenge - how to flash around the vent stack. I've seen rubber gaskets used and I wonder how they hold up compared to comparable vent-stack flashing used for 3-tab asphalt roofing. Any ideas/suggestions/comments would be greatly appreciated. Thanks,Eric.