Step 1: Parts
To make a Lego ball you're going to need some Lego bricks (duh). You're actually going to need those flat bricks called plates that are about 1/3 the height of a normal Lego brick. You will also need what Lego calls a 1x4 brick with 4 knobs which is basically a standard 1x4 brick but with an extra set of studs perpendicular to the ones normally on top.
I'm including a parts list of the parts I used in this Instructable so that it will be easier to understand. Of course you can always substitute for parts that you don't have with ones that you do (like using two 2x4s in place of the 4x4 or using two 2x4s in place of the 2x8) but just be cautious about maintaining structural integrity. I know rainbow warrior (using bricks in any and all colors) is sometimes the only option but the shape of the ball shows up better in solid color so if possible, try to stick to just one color.
-8 1x4 bricks with knobs