This is the head scratchinest part of a deck.
I guess I didn't take any pictures of how I measured the cuts. shame. that might have been useful to someone, and it would actually take me 1000 words to describe how I did it.
cliff notes version:
You take a 2x12 and lean it up outside of the edge of the deck, then use a level to make a horizontal line from the outside corner of the bottom of that board before you move it. cut that line. this gives you the ability to set it down on that cut, and strike a line where it meets the deck. cut that. You have to figure out how steep you want them first, and allow for 6-7" risers and 9-11" tread depths. ( this is running right down your face, right?) also, leave a notch so you can mount them....
blah blah blah..
anyhow... here are the stringers all next to each other, and temporarily screwed to a couple plates to secure them while I cut a channel that I will use to mount a brace:
So I use a circular saw and cut a bunch of cuts with the blade set to the right depth:
then I break off all the bits left, and chisel it smooth:
