When should I consider using Plastic Round Cap Roofing Nails

The aluminum is probably more susceptible to denting, being a softer metal.

Will you ever need to walk on the roof? Do you have overhanging trees that may drop branches in a storm? Even trees near your house can see branches go flying your way.

Another question is the coating used. Since steel can rust, you don't want to worry about it. A high quality product would seem valuable there. Of course, you don't want to see paint flakes peeling off an aluminum roofing product either.

Finally, make sure that you can deal with snow, although this is not a factor that depends on the material itself. Our neighbor has a metal roof. A few years ago, we had a large, heavy snow fall, and a huge mass of snow broke free to slide off the roof. As it was coming down, it tore off the gutters on their home, then completely flattened part of their porch. My guess is it was several thousand dollars worth of damage. Falling snow can also damage plantings near the house. There are tabs that can be placed on the roof surface to prevent this if you live in the snow belt.

Here is what I ended up doing:

The entire roof had an ice and water shield that was sticking the shingles. This guy's write-up about his roof closely mirrors my situation in that it was south facing, low slope, and old.

After deciding to just lay shingles onto the remaining old shingles, I noticed that the sun warmed up the substance to the point where it was relatively easy to peel off the stuck shingles with the roofer's spade. So I got the old shingles off, put down felt and applied new roof. Thanks!