I used scrap pine boards from another project:
x4 - 4"-1"-16.5" (For the step tops)
x2 - 3"-1"-15" (For the front supports)
x1 - 12"-1"-15" (The back)
x2 - 12"-1"-14" (The sides)
-Appropriate Safety Equipment for working with power tools and dust.
-Kreg Pocket Hole Jig
-1 1/4" pocket screws
Step 1: All The Cuts
Step 2: Drill The Pocket Holes
I recommend doing a dry run on assembling your project by just balancing everything together. This way you can see where all of your prices will join up and you can mark where you will put your screws.
Depending on how you wish to finish your project you will definitely want to sand your pieces when your holes are drilled and possibly stain or paint before you put everything together.
Step 3: Putting It Together
Start by securing the bak piece to the sides.
Flip the stool over and attach the top steps working your way piece by piece to the bottom step and brace.