I actually created a pokeball when I first started like 1 month ago :/, was going to make a pokemon massacre for shock value purposes but never got around to learning how to rig the &%$# characters. Anyway, heres a pic, yes i know there horrible and i still ask myself how I created a Bad pokeball but somehow i did. there pretty cartoony lookin!
but as for your questions
if using polygons i suggest scale in the middle faces of the sphere and extrude them inward to get the middle line, and your best bet would be just be to make a small thin cylinder for the middle circle. You can use Ramp shaders (by going to Window-rendering editor-hypershade- click Phong - go to its color settings, pick Ramp and adjust the color there if using 8.5 or 8.0) and set the color there. Also the Phong will give you the shininess you need. But Im guessing tammy had that in her post. This is the pokeball I created 1 month ago, its unrealistic so im sure youll blow this one away disgustingly...