21 9 0 and 9 21 0 are better than taking utlity, as you benefit little from it. The only good things there is death timer reduction, exp gain, movement speed, etc.

Your item build isn't all that good. Besides Tabi, Gunblade and Guinsoo, your build isn't good. Atma, Rylai and Sunfire are weak items, and you'll still have weak MR. Atma's Impaler stacks once with your passive, but besides that, nothing. Rylai is good, but from your playstyle, you'll hardly chase any champions with juking skills. Empower Leapstrike may not always be good. Sunfire does damage via a small AOE around you, but its still too weak. Your damage and AP are low. You may want to build on that.

Also, your guide talks quite little on several specific points of the game.

Hope it helps :)