Are you a licensed contractor WITH insurance? Do the homeowner a favor and don't do it without insurance. Steep roofs and second story jobs aren't for beginners and it scares some experienced roofers. Remember you also have to carry 80 lb. bundles of shingles up with you as you work. I'd hate to see you try to start the job and then find out you can't hack the steepness especially if you are already worried. That is why roofing companies charge extra for steep roofs and it pays for the extra equipment they need.
They make roofing jacks to hold 2by4s to step on. You need enough to keep what you have and add more rows as you move up about as far as your reach so it takes a bunch of them. Get a safety harness and tie a rope around a chimney incase you slip. Have a helper around to call fire rescue, etc. if needed.
On a steep roof, it is nice to start with scaffolding to walk along and do the bottom rows. You can rent or build the scaffolding. For the roof, we used to get a bunch of 2by4 by 12's and lay them in a row. Every 3' or so along the row nail a long roofing nail(hopefully into a rafter) in the same area you nail shingles. Leave the head up a little and wrap a 3' piece of wire a couple times around the nail. You then have a series of 2 tailed wires hanging down to tie around and hold your 2by4. Keep all rows in place to stair step up and hold shingles when you get to the top. When done, lift up the shingle, remove the wire, and then hammer the nail on down removing each row in reverse order. Good luck.