Ap, Magic resit, Armor, AD?

[quote=TheNaethryn]Hi all! i am working on my own Sion build right now because A). Sion is the only character i am remotely good with and B). i don't like following other people's builds (i feel like that makes you narrow minded) and i have stumbled upon a problem. I am in a tug-of-war with cool down reduction, AP, and Magic pen. The biggest problem is i have no idea how magic pen and magic resistance is actually calculated, nor do i know how armor and armor pen is calculated. Therefore i also don't know when i need to get one over the other and this is probably pretty important stuff :D. If someone could explain this too me or give me some kind of example or ratio i would really appreciate it! Thank you![/quote]

[quote=Mowen]http://www.mobafire.com/league-of-legends/forum/theorycrafting/lvxs-theory-crafting-compendium-game-mechanics-and-effect-maximization-197 My links go rawr![/quote]

[quote=Jebus McAzn]In plain English: As AP Sion, you probably already use Marks and Quints of Insight, and you probably get Sorcerer's Shoes every game. So as a rule of thumb, get some flat AP for most of early/mid game. Once you see enemies starting to get magic resist, or once you've completed your 4th item, build an Abyssal Scepter. In most cases, you'll want to stay away from Void Staff. CDR really isn't all too useful on Sion.[/quote]

[quote=Mowen]He's not level 20 yet, at least not since I saw last. Just want to reiterate don't buy runes till you're level 20 so you can buy tier 3 runes! :)[/quote]