YOU CANNOT STAND ON A STEEL ROOF TO CLEAR IT...
SNOW ON A 3.5 X 12 PITCH WILL NOT SLIDE!
I can surely tell you, you cannot walk on a snowy metal roof, you will go for the ride of your life.
About the pitch/slide, there are variables - compass direction is a big one, heat or no heat in the building, heated building with insualted attic space, etc.
I know duffster loves being a contrarian (I too have low pitch metal roof and it will eventually slide) but all other things being equal, the 5/12 roof will clear before the 3.5/12.
I should add, the winter of 2007-08, I had multiple layers of snow ice about 1-2 foot deep, it was so locked up, it wouldn't slide on it's own.
Dave.