Take InterNACHI’s free, online Inspecting the Masonry Chimeny Flashing Online Course.
I just took this course. I did not like that the step flashing used did not have a good overlap, only about 3/4" overlap. and did not like that with the counter flashing they folded it towards the front instead of cutting it off and adding the rivets on the sides. the fold overs look really amateurish. I have flashed probably 100 chimneys in my time doing repairs, roofing and general contracting over the years.