I started to play Orianna and I want now to share my build. This build is good for mid, solo top or laning with a teammate.
What can you expect from this build ?

You will make a lot of gold by killing creep. I'm always the first of my team. I already killed more than 450 creeps in less than 40 minutes.
You will have a great survivability. Gank Orianna is very hard, tear of the goddess and clarity give her the ability to check grass as she want and you have a lot of health point.
Your control will help to chase, run, gank, recon and confuse the opposite team. In addition you make great AoE damage.
At lvl 16+ you will save so many live by spamming protect. With a good stuff you add more than 500 HP every 5.4 seconds.
Finally, you will do so much more. Your ball give you so many opportunity.

Pros :

Great harasser
Good control
Good AoE
Great ult
Good support
Good ranged attack

Cons :

Will be focused by all assassin.
Slow movement speed
Hard to master
Don't make coffee

Mark : Greater Mark of Magic Penetration, I see no others runes here for this build.
Seal : Greater Seal of Scaling Mana Regeneration. You will manage at start with clarity and teleportation. (don't forget to buy tear of goddess the sooner as possible, when you have enough gold, just be aggressive, use all your mana and back + teleportation.)
Glyph : Greater Glyph of Scaling Ability Power or Greater Glyph of Scaling Magic Resist. You won't need cooldown reduction, boots and potion are enough. (And let blue buff for an other one. You don't need it.)
Quintessence : Greater Quintessence of Scaling Ability Power or something usefull like Greater Quintessence of Movement Speed or Greater Quintessence of Scaling Magic Resist.

Archaic Knowledge , then utility. You have no other way.
Of course, take what you need for your summoner spells.

My first advice : Don't rush ability power and magic pen. You will make damage by harassing, having a lot of mana will be your way of making damage and having a lot of HP will prevent a deadly tower diving. you will make gold so fast than you will have all you need for end game. Just be patient. Of course, don't die, you can't or you won't make gold and you will be the weakest champ of your team.

Tear of the Goddess first or you will be mana dependent, so make a Meki Pendant. Take 2 Health Potion, it's definitely a big advantage against Doran's Ring players for Orianna. Boots for harassing and escaping. (If they have Brand, it can be a good idea to buy Boots first.)

Riley's Crystal Scepter, will give you control for gank, harass, escape. HP and ability power. I will never start with an other item with Orianna.

Ionian Boots of Lucidity and Catalyst of the Protector. Buy a Blue Potion if you have enough gold. +25% cooldown reduction, with your masteries you should be near 35%. That's it, you are now one of the best harasser and can move your ball every 2.6s.

Now take an Oracle if they have a teemo, with your ball you will be able to check grass and destroy mushroom or ward. Check your jungle, and your team will never be ganked.

Make a Rod of Ages, if they have LeBlanc, Annie or something like them, change it for a Banshee's Veil.

They will start to have magic res, it's time to make a Void Staff. Then just end this build with Rabadon's Deathcap and an Archangel's Staff.

You make now insane AoE, control map, support your team, croud control and have 3K HP. Just have fun and let some kills for your teammate.

Teleportation : You can handle 3 champ at least under a towr and you will enjoy to kill a huge wave of creeps.

Never be afraid if you can save a towr. Teleportation->Q->R->W->Q->E->Q. You will instantly kill all creeps, stun champions, deal a huge AoE and the towr will be able to focus a champ. If it's work you will be feed enough, and if not you should not have any problems to run.

Clarity : I can't play without it. I spam my skill every time they are available. You have at least always a grass to check.

Ghost / Flash : It's always good to improve your escape mechanism.

Fortify / Health : Can save your ***.

Exhaust : Can be good against a Xin Zhao chasing you, but seriously, if you play it well, it will never happen.

Upgrade Command: Protect in last. You will need to have a lot of ability power for it, and you will ! But 80 HP for 4 second isn't enough at start to spend your points in.

So ? What skill you have to upgrade first ? Command: Dissonance deal better damage. But Command: Attack have a better cooldown (4s at level 5, 9s for Command: Dissonance) and use half less mana.

So upgrade Command: Attack. With it you will kill all creep of each wave at lvl 7 with Q->W->Q AND harassing champion. Throw your ball on mages creep. Kill them with W. Then kill fighters with Q. Then, check grass and if it's safe. Harass them !

Of course, spend 1 point in your ult at level 6-11-16.

Orianna can use all of her skills without stoping herself to move. You will have to master them to be a good damage dealer, she is not a right click to win champion.

If you go too far of your ball, they will come back to you.

Command: Attack The first target will take 100% of damage and it will be reduced for each additional target with a minimum of 40%. Send your ball behind creeps, then you will be able to make 100% damage on champion. If they come to close, just back, your ball will be out of range and come back. Then harass to hit champion first.
You can use Command: Protect to get back your ball but it's not necessary, you will always play far enough of your ball and having a total control on it. It will fun to use it for kitting with your Riley's Crystal Scepter.
Use it to check grass.

Command: Dissonance It deal damage near your ball, the AoE is a litle larger than Command: Attack. So it's not because you didn't hit your target with your Q than your W won't.
Care with it, sometime you will be too far, the ball will back and you will fail your W.
While running, use it on your way or on yourself, don't kit with it while running if you need speed.
While chasing, send your Q then W, you will enjoy it.

Command: Protect Add HP for 4s. Move your ball on the selected ally champion and give him resist. Deal damage on his way.
If you not master it, just use it on the focused one. You will have to learn how to use it for deal a litle more damage and activate your Riley's Crystal Scepter

Command: Shockwave. This skill is awesome. It will deal AoE damage, throw champions over the ball and stun. It will stop Katarina, Malzahar and Nunu & Willump's ultimates.
Use it to chase, to run or control teamfight.

I will distinguish two situations, if you have a team for 5 vs 5 teamfight or a team with high ability to gank.

5 vs 5 teamfight :

You have to force the opposite team to fear every grass. Force them to fight your team on their line. When you push, check every grass one by one throughout the game. Mid is good for this. Kill creep fast, and check grass.
Here your road to prevent gank. Do it at each wave if you can. Go bot only if they are in trouble. And never go alone in the crossed area.

During mid game, you will have to push. Stay behind and build a safety zone. Let your team move forward. Check like this picture.

Kill ghost by the way.

You can see i check only the west side while pushing mid. It's offer you the best way to run. You have a good control which offer you a good escape mechanism but in a short distance. You are slow never forget that, mid is the best way for you. Push top and bot line only with teammate if you have advantage, if not, be ready to run with your mate. Check grass and jungle to be sure no one take your back. And use your W to run at the first sign of ennemy.

In my opinion, the east side offer too many wall and not give you advantage

Let's start the fight. If they are stupid and focus tank, please yourself, send your ball behind the ennemy line where it will affect the most ennemy. Use your ult. Melee char will be throw behind the ball. And Ranged will be throw before. They are all stun, use your W, you will damage all of them and slow them for (45% skill, 15% riley) !!!! Use Q on the weakest champ and your E on an ally in need. Then kill them all.

If they focus a weaker char send your E on it. Use your ult then Q behind him. W them, they will take a lot of damage, will be in range from all of you will slow them and will provide +45% speed to run if he need. If you are winning the fight, start to harass and move forward to cut off the retreat. I tryed to draw something to show you how the ult work. Red is orianna, blue the ball, black hostile champ, and orange your teammate. They will be throw along the dark line. (I hope it will make you laugh XD)



Gank Team :

I will give more detail later but the work is the same, except you will have to fight behind the wall, never show yourself. check the champions ambushed behind wall and focus weakest champ, use your ult to throw support champ in fight.

Annie :

Be carefull of flash / ignite combo at her level 6. You won't have any problem, harass her.

Brand :

Both have ranged AoE. Buy boots and be smarter. You have no other way, he won't forgive your mistake.

Karthus :

Buy boots and kill him. You can't lose. =D

LeBlanc :

If you see her come to you before her level 6, she will jump and use her Q. Don't be afraid she will be focused by creeps so move forward auto-attack her then Q-W.
Be carefull at her level 6.
She don't kill creeps fast enough to be dangerous.

Lux :

Maybe the worst champ for you. If she harass you, be far of your creeps, she won't make gold.
Wait she used

Lucent Singularity before acting.


Malzahar :

Get away from

Malefic Visions, be carefull at her level 6 if he have flash and he won't be a problem.


Morgana :

She have skill vamp and can root you. You won't kill her, so make last hit.

Ryze :

Kill him. XD

Shaco :

Your Q will destroy

Jack In The Box so i suggest you to help your jungler and to be in the lane where shaco are. If he try to trap you, send your ball in grass, if you got some gold, the way is clean so just kick his ***. Seriously, a shaco AP is a joke if you have Orianna in your team.


Teemo :

Make your

Rylai's Crystal Scepter then buy an oracle. Clean your jungle and grass at top and bot lane from mushroom.
Do the same if they have any warder.


Vayne :

If you manage to take away half of his life and preserve yours. You won, if not, she will kill you so just make last hit and wait. Vayne with boots + potion is realy effective against orianna or brand.

Veigar

Get HP, be smart, make him cry. If he don't stun you, he will never hit you.

Vladimir :

One of the best mid champ.
Early game, you will have a big advantage. Your range and your cooldown. Harass him, don't be afraid, kill creeps. Don't let him have last hit. You must delay the purchase of his

Hextech Revolver or you won't kill him after this and he will start ganking and tower diving.
If you do it well, he will have to back before his level 6, and maybe kill him.

Orianna is not the best damage dealer, don't have a burst like veigar, but she do so many things than she can be the main support of a team and a great 5 vs 5 fighter.

A last word, my English should be bad, i work on it. Hope it is readable and i beg you to forgive my mistake. Of course, correct me if it please you.