James wrote:
I have thought of using the rubberized WeatherGuard instead of felt. Is
this better than paper felt? Although I think it would be quite expensive
for a house, just 1 roll would do for my shed.

If the additonal expense doesn't bother you then I say go ahead.

What size nails would I get to lay down the WeatherGuard ?? Would it be
the same type nail as the nails for the shingles ??

That stuff is self- adhesive and requires no nails. You just peel off
the backing and it sticks to the deck like glue. This is one of the
big advantages of the material.