If your talking about using blocks for your risers, then use a standard
8x8x16 block but set the each riser block deep enough to give you the rise
that you want.
If you already have a footing, the you will have to cut down the height of
the first (lowest) riser blocks.
I've done this when putting in crude steps, leading down a hill side. The
just pour a tread cap on top of each step to tie them together..