I recommend changing the build item, as nashors is god awful on Sion, using the money to buy a defensive item, or even more ad would be better. Also 0 points in defensive tree as ad sion is suicidal, his early game softness and anti-sustain is hell. 2 PD is big waste, when shiv is here,1 pd and 1 shiv is better, also allowing for early avarice blade.

Also don't write a guide, if you don't have options to the most optimal runes.
Those are just some of the problems with this guide, also doesn't go in depth about items to build in lane to counter(GL trying to get sion to late game without any counter building, have fun vs jayce with no armor, POKE POKE POKE).