If I am not mistaken, i do believe that you are wrong in one aspect. You cannot get your opponents mr or armor below 0 so any bonus pen or reduction is useless and a magic ability that does 100 damage will do 100 damage to a target with 0 magic resist even though you may have magic penetration runes or anything else that might lower their mr.

that rocks, maybe a lil bit expensive gold managemend but thats ok for ranked

17/2/8

Good build, had a game with the build you made, got 12/4/5

But Didn't use the same masteries as you had used for yours, all in all good build, well rounded for him with his ult you get a thumps up :)

Be kind and dont flame !