Point taken, deathfire grasp is a viable choice sure but by end game your AD champs should be rocking Madreds and last whisper if the team is that heavy with tanky characters so Rylais would be more beneficial so you can slow the target while dealing massive damage. That way if your burst doesn't end up killing them your teammate will be given the opportunity to do so. Also if you already have Void staff your damage output is already hightened. I'll definately try it out next time the chance presents itself and I'll add it as another viable choice for Tank Heavy Teams. Like I said in one of my Variations section, there is always room for mix and match.

Great build man!
The only thing I would change, because it has happened to me on several occasions, is switch out Rylai's Crystal Scepter for Deathfire Grasp for when facing against heavy tank/bruiser type teams. Reason being, though Rylai's gives you the 500 Health and Slow Effect, Deathfire Grasp in my opinion was made for destroying tank/bruiser's with the '30% of their current health (+3.5% per 100 Ability Power)' effect.
Will definately try out your build when I play Orianna.
+1
Cheers!

I've Updated a couple things.

Thx Pacho. I know it's not as descriptive as some of the other guides out there but if people are willing to give this build a try I'm sure they will come to the realization that Orianna can be a very rewarding and ridiculously fun champ to play as pure offense. I remember one of my first games with this build I had become so fed that after getting blue buff on enemy territory I was hiding in bush getting prepared to teleport back to base.
Apparently the enemy had wards up around their buffs so 3 of them came charging down after me. It all happened so fast all I remember thinking was oh ****, tossed my ball into them and did the ult combo thinking I was going to die anyway might as well go out swinging. Well, it killed two of them straight away and the third was a tick from dieing so i finished him off with an auto attack. That was the end of the game, they surrendered and that's when I fell in love with Orianna. lol. Now she's one of my mains and I'm kicking myself for not buying her even sooner.

Anyway, gl to u too, hope you enjoy the build.

I'll use when I will buy my own Orianna.

Nice guide dude. I love Orianna (only if you rae playing her like a damage dealer not a support). Its a great guide. Good luck! xD