Hi, I'm Arkhan Iyusu, a Platinum-Diamond leveled Orianna main on EUNE. Since Orianna is by far my favorite character since Season 3, I've been experimenting a lot with building her troughout the years. However, I've never been motivated enough to make a serious Experimental build (guide). (If you want a serious standard build and an In-Depth guide for her, check out 'LadyOfClockwork''s guide here on MOBAFIRE. Link: https://www.mobafire.com/league-of-legends/build/the-lady-of-clockwork-we-are-as-one-in-depth-421873 This is by far the best guide for her I've seen out there.)

IMPORTANT! Since this is really an Experimental build, no alternatives can be set regarding the item build, nor the Keystone rune. I ask those, who care enough about this, that try this out in a normal game (2-3 times) if you will and give me and other interested players some feedback on this build. Thank you!

Flash - Barrier
Flash - Ignite
Flash - Heal

All are good choices, depending on matchup/personal preference.

Skill order: E on first level, then R > Q > W > E

E on first level helps you to trade only with autoattacks straight up in lane, since Glacial Augment will slow your enemy and Orianna's passive, Clockwork Windup is one of the best early dueling skills in the game.
Q on first level, however, will give you the ability to keep the river under surveillance without putting down a ward, thus preventing invades or making them think twice. First seer takes the deal in LoL. This is a very handful ability and MUST be abused whenever possible.

Let's be straight-forward:

Runes are: Main - Inspiration (Glacial Augment, Perfect Timing, Biscuit Delivery, Approach Velocity), Side - Domination (Cheap Shot, Ingenious Hunter)

Explanation:
Keystone: Nothing special here, it is one of the core elements of this build. It gives you enhanced basic attacks per target per 4 second AND enhances your item build.
Perfect Timing: You'll build Zhonya's, so it's pretty self-explanatory. You may pick Magical Footwear if you really want.
Biscuit Delivery:To be honest, I used Minion Dematerializer mostly, but that's really a self preferance. BD will give you more sustain in lane.
Approach Velocity:It combos with your huge amount of CC and permaslow. Also very helpful if you want to save a dying teammate. Cosmic Insight is the community's favorite, so take if you really don't want to listen to me, your choice here.
Cheap Shot:It has a 4 second CD, but I assure you, every of your attacks will proc it early-mid- and lategame.
Ingenious Hunter:You'll be able to use Zhonya's and GLP more often, which adds to your survivability and reliance on this build.

Simply (in order): Hextech GLP-800, Zhonya's Hourglass, Rylai's Cristal Scepter, Liandry's Torment, Void Staff + Sorcerer's Shoes (whenever finished).

Explanation:

Hextech GLP-800 gives you a huge AOE slow and some dmg, which is also enhanced by the Glacial Augment. 60% AOE slow is not to be ignored. It could catch off any enemy champion, or even turn the tide, just like your ult. (However, since it is not built from Catalyst the Protector anymore, it does not give you that crispy sustain anymore either :S ) Morellonomicon was a boring item anyways, I'm glad that they reworked it completely.
Zhonya's Hourglass: Gives the last amount of CDR we need (30% is pretty much enough to spam) and gives us the most OP active of LOL nowadays and now it's even enhanced by Ingenious Hunter. IF you didn't choose Perfect Timing AND don't want to (or can't) build, because there is no AD enemy/too much AP enemy, build Banshee's Veil. However, stick to it in any other case to serve the experiment.
Rylai's Crystal Scepter. Oh boy, the CC comin' out! Build it to top off the never-lasting slow you curse your enemies with! Good against agressive bruisers and also some assassins.
Liandry's Torment is the final item, but by far the best option you have to finish your build. By having this item with this build, every of your abilities will cause the enemy the BURN their MAX HP's 2% every SECOND! It also gives you survivability and lots of AP, but no Magic Penetration anymore.
Void Staff is the very final item you want to get. You'll get that 40% Magic Penetration. It literally shreds any tank. Since you won't have that much AP, you'll need something that reduces magical resistance, just to compensate the build's disadvantage of having mediocre magical power.
Sorcerer's Shoes. Since you won't have much Magic Penetration, you have to compensate. If you don't see the need of it, since there is not enough Magic Resist in the enemy to really chop your damage off, go for Ionian Boots of Lucidity to have the crispy 40% CDR. Or go defensive with either Ninja Tabi or Mercurian Treads.

Pros:
-Huge AOE CC
-Mediocre AOE damage
-Good survivability in all phases of the game
-Mediocre DOT-damage
-Not much of a counter-play to permaslows can be found.
-Good teamfighting-power

Cons:
-Can't oneshot like normal build Ori(until fed/hilariously ahead ofc)
-No mobility
-Weak early damage
-Needs her team even more than simple Orianna

Thank you for reading through all this guide and explanation! I humbly ask you, if you were interested enough to read all this, go and try this out for 2-3 games and let me know if it worked for you!

Make sure to rate and comment appropriately and give me/us feedback on this, if it worked/failed. It will highly be appreciated if you even gave details about the game itself (teams, champions and the matchup itself.) Thank you!