I've got a story and a half home with a 9/12 pitch roof so during the winter months it is almost impossible to climb up to drop a brush down the chimney. So, many years ago I made a bracket that fits on top of the chimney with a pulley in the center and another on the outside edge. I have a 3/16ths stainless steel aircraft cable that makes a loop from the bottom through the two pulleys and back down again.
I open the clean-out door on the bottom, shove a brush in that has a cable attached to the bottom, and pull it up with the looped cable and pull it back down with the cable that is attached to the bottom of the brush.
Once in awhile I have to be ready to close the clean-out door if I hear some soot falling so I don't get a face full of dust!!
Works good and I don't have to climb on the roof, worry about falling off, and taking years of wear off the shingles.
BTW, for my own mental well being, I like to clean the chimney every two months during the heating season. I get a good feeling when I can pull the brush all the way to the top with no resistance and only about a quart of soot falls to the bottom.