Thaniel went over quite a bit of what needed to be brought up, so I'm not going to vote just yet to give you time to situate things. One thing that I thought was unique about your build was the hp5 Quints that you use. That could open up some pretty nice opening for Orianna considering that is one of her weak spots. Good find and keep up the good work.

O and one last thing I beg of you is to reconsider the Zhonya's (maybe throwing it under "Optional/Situational Items" or something)... I just hate that item for Orianna, I'd rather see a Lich Bane, Mejai's, Manamune, Nashor's Tooth, Frozen Heart, or even a Rylai's over it.

I main Orianna, so I'm familiar with when and how she uses her mana. In the current metagame, you're unlikely to lane anywhere other than solo top or solo mid with Orianna, and that is why I believe she needs more mana than your build grants her.

Sure, you can stay in lane and get creep kills without using too many spells, but you allow your lane partner to do the same, which is just what they want. Once you've allowed them that, they'll just float down to one of your less fed characters in bot or top lane and pick up an easy kill; maybe first blood.

I say she needs more mana regen early because maxing Dissonance as I do costs more. I see you've chosen to max out your Command:Attack first. Why have you done this? From my experience, Command:Attack is a very mana inexpensive ability, but it also does nothing in terms of early game damage. It also doesn't boast the slow that Command:Dissonance has, and therefore won't allow you to follow up your harass with 2-3 auto attacks before returning to creep kills. This leads to less lane dominance overall and lets your opponent (for the sake of the conversation, let's say it's Cassiopeia with 2 in her Twin Fang and 5 in her Q) dominate your lane with their superior harass.

On top of the mana required to maintain harass, it's usually a good idea to use some mana in order to secure creep kills when laning against an opponent who you can't force away from your creeps. (Caitlyn and Corki are good examples of this with their long range) Without the extra mana cushion, you're very likely to be outdone in CS, leading to your team having a worse endgame because of your ill performance in mid.

hey thanks for the comment, yeah at first i noticed i had trouble managing my mana early game. but once you play a game of placements and patience you'll notice that she doesnt need as much mana as everyone says she does. basic mana regen seems to work well with my play style. grabbing void staff as my second item is also out of the norm, however i use ori as mostly heavy burst and support. she has enough sustainable mana to hold off most attacks and contribute to wiping out the team. i generally dont spam my spells during fights but rather wait for the right placements or set up for the best opportunity to strike. i have yet to have severe mana issues with ori. feel free to try out my build and try playing with more patience in mind while keeping a sustained harass game.

again its only my first attempt at building a guide so more comments and criticism will greatly help

I voted -1 for now. Clarity on Orianna is not optimal, and your build doesn't afford her any early game dominance through Magic Regen or early AP. Rushing a Rabadon's makes sense on some champions, but is pretty lame on Orianna. Sure your spells will be stronger than most other champions on the field, but you'll only be able to cast them around five times before you're OOM... And being OOM without very much Mp5 is a trip back to base.

Grabbing Void staff as your second item is strange because, again, you're building her as a mage but ignoring her need for mana. At the point in the game where you can afford a Void Staff, you're going to need survivability and sustain more than anything. The way you've set it up, she'll have neither.

Finally, building Archangel's Staff all-in-one at the end of the game is ridiculous. Orianna is a very mana hungry champion, especially early game, so to not build her a Tear of the Goddess when planning to craft an Archangel's Staff lategame is an amateurish mistake at best.

It seems like you're using a rather useless summoner skill (clarity) to make up for the fact that most of the time you'll be OOM due to your shoddy build order, and because of this, you're going to be dominated in mid the first time you face off with any competent summoner. At least, you will while using a build with no Mp5, no survivability until endgame, (and even then, it's listed as optional) and a weak summoner skill trying to hold up an overall bad design.