I use this build just to bully my lane. Also it allows great late game ap and health. When i start i start very causious and just bully behind minions so enemies cant get exp and/or gold. Last hitting isn't really key but with the pricey items needed it could help. Build works better either teamed up with a melee who cant farm, Warwick is an example, or solo mid.

My runes and masteries help me with AP, cooldown reduction, mana regen, and health regen. These come pretty handy early to mid game.

The items can be in any order and what ever you want it to be. But for my build the order goes: 1. Meki pendant- for abusing the attack ability Orianna has.
2. Health potion- just so if i get beat i can recover and stay in the lane longer.
3. Speed boots- to start chasing and running away because by now you have 3 abilities and must start pushing
4a. Health potion- just in case enemy team is beating you down
4b. Ionian boots of Lucidity- when you recall to get these items make sure you have enough for these boots and your next AP item
5. Blasting Wand- With this item farming with your dissonance ability will be easier.
6a. Saphyre crystal- Only if you need to recall and dont have enough for 'catalyst the protecter'
6b. Catalyst the protecter- so while you lvl up you are refunded with health and mana
7. Rod of Ages- its passive helps the longer you have, its cap is ten minutes with the item, very handy.
8. Tear of the Goddess- by now a skilled player should be ganking and just plain out last hitting or farming (by now your lvl should be around 8-11)
9. Archangel's Staff- for great amount of mana and mana/regen
10. Rylai's Crystal Sceptar- Begin this item so you can last longer in team fights and so you wont be so squishy and wont be picked off in team fights. Also it slows your enemies with just the Attack: abillity then for a greater slow you use your dissonance abillity for great assisting (by now your lvl should be around 12-15)
11. Rabadon's Deatchcap- even though it has been nerfed it still is a great AP boost so now instead of assisting, i usually get more assists than kills, you start racking up kills.
12a. Void Staff- just for that extra kick against enemies
12b. Banshies Veil- If your enemies are picking you off or just hitting you with some harsh damage build this item for its great abillity to cancel one negative spell. Usually go with this one just in case enemy team gets baron.

Overall this build is handy for early and late game battles. The items can be built in different orders, for example you can rush for AP if your not great at last hitting, so therefore you farm with the dissonance abillity. There are other ways to build orianna you just gotta test them out and what ever makes you comfortable and/or makes you dominate. The summoner spells are just to help with early game kills. you can subsitute them for flash and/or ghost, other summoner spells handy for this character.