Welcome to my guide! This is my first guide and I'm pretty bad at english so just follow the guide to get high eloz! XD

Your item purchases on Orianna are very situational. I almost always rush grail, unless you need the mobility to either dodge skillshots or gank lanes more efficiently, you would go sorc boots.

If you are getting bursted down, rush negatron after grail and build into abyssal, otherwise build rabadon.

I usually build orianna as a off-tank caster with max cdr, maximizing her utility and dealing decent damage.

Usually I go rylai for the sustain after rabadon or hourglass if I am still getting bursted down or am currently losing the game.

Your last item is also situational, if you think you are tanky enough to stay alive in team fights then get void staff to maximize the damages. Otherwise you can get guardian angel for even more tank.

So good luck summoners and win those free eloz with beautiful Orianna!!