In Oregon at least that won't pass code.
We are required to put a 6" thick concrete pad under each hole that is 18" in diameter.
I believe we are limited to 1500lb per sqft load and a roof snow load has to be 20lb/sq ft..some simple math and yu get to the 18" holes.
I used a pst hole digger and opened them up with a shovel..OK for 3 or 4 holes but no more.
Frank