Technically speaking, an 8" step is illegal. At least all residential codes that I'm aware of cap steps at 7-3/4", there's also a minimum I think but I can't recall what it is off the top of my head. I know, nit picking, but it'd be a pisser to have someone (code official) stop by the house and check and make you rebuild them.
And just a quick add to Steve's excellent instructions, a 2x8 is actually 1.5" x 7.25" so if you use a 2x8 + 3/4" plywood you'll end up with an 8" step. If it were me I'd rip all of the 2x8's to be exactly 7" deep since you're likely to find that they vary between boards by an 1/8" or more which is easy to lose in a floor but harder in a small platform like that.