Quintessences\Marks - AD - Standard runes for almost every AD carry. Gives you damage for last hitting, poking, harassing.

Seals - Armor - Allows you to reduce damage taken from opponent's AD harassment during the laning phrase. Gives more survivability too.

Glyphs - MR\Level - Reduces AP damage from AP casters that would try to burst you down with spells.

Flash
Standard Summoner Spell for almost every champion. Allows you to escape from dangerous situations and make plays too.

Barrier
To be used trading or blocking incoming burst damage. Can be use to bait enemies as well

Doran's Blade - Probably the best item and cost efficient item for any AD carry currently due to the 10 AD, 80 HP and + 5 HP on hit passive it provides.

Blade of the Ruined King - This item provides 3 important things to an ADC. Sustain (Lifesteal), Damage and Attack Speed. It has a passive that synergizes well with your Vault, allowing Quinn to quickly burst down squishy targets with a single combo combined with this item's passive. There little doubt that this is the best first big item for Quinn.

Berserker's Greaves - Standard boots for AD carries, more Attack Speed, more DPS.

Infinity Edge - After completing your BOTRK, you can start buying high attack damage items to turn Quinn into an insane DPS machine.

Phantom Dancer - Gives Attack Speed and Critical Chance you need to synergize with your Infinity Edge. The small movement speed bonus gives Quinn slightly more kitability too.

Frozen Mallet - I usually build this as my 2nd last or last item, as a semi-defensive item. It gives a decent amount of damage, huge amount of health and also provides your auto attacks with slow.

Last Whisper - Buy this to shred through champions with high armor. Provides Attack Damage too. Buy this before PD if you notice enemy champions stacking a lot of armor.

Pros
Good Mobillity
Can do good harass using her passive
Gap closer/Ministun with Vault (E)
Has blind - Allows Quinn to win trades 1v1 with Auto-attack reliant champions
Your W gives you a huge range of vision - good for scouting/facechecking, allows

Cons:
Mastering the use of her skills in different forms can take some time to get used to due to shared cooldowns on Q,W,E in both forms.
Risky to play in Melee Form as Vault (E) brings Quinn into melee range to her target .
Low Auto-Attack range

Early Game
Quinn should focus on farming creeps during the early game, just like any other ADC. You might occasionally harass with Vault and auto attacks, but concentrate on farming up for your first big item, BOTRK. Poke effectively wisely decide whether and go for kills if your support decides to initiate. The basic rule for Quinn's early game is to get as much CS and farm as possible for your items.

Mid/Late Game
After Quinn gets farmed and gets a couple of big items, Quinn is able to out trade and duel champions one on one with ease. Quinn also provides utility with her Heightened Senses (W), which grants your team important vision even if it is just a few seconds. With your wide range of abilities and utility, Quinn is able to adapt to situations and many types of teamfights. With her attack speed steroid and blind, Quinn is able to deal massive amounts of damage and also avoid taking auto attack damage. Like any other AD carry, positioning is key to playing Quinn well.

Do not be mean, it's my first build