This is my build the way i think is the best for Ashe.

Boots of Swiftness

UNIQUE Passive: Enhanced Movement 3. With any other boots you would be too slow. And you are in need of speed

The Black Cleaver

30 Attack Speed, 55 Attack Damage. Passive: Physical attacks reduce your target's Armor by 15 for 5 seconds, (maximum 3 stacks). The item has exactly what you need. Attack speed, attack damage and armour penetration.

Stark's Fervor

20 Attack Speed. UNIQUE Aura: Gives nearby allies Champions 20% lifesteal, 20% Attack Speed, and 30 Health per 5 seconds regenerated. Reduces the Armor of nearby enemy champions by 20. This item is great because it gives you an essential amount of attack speed combined with The Black Cleaver so you dont need to buy Phantom Dancer. And since you are carry in the game it gives lifesteal,attack speed and health reg. to nearby allies.

Trinity Force

30 attack speed, 30 attack dammage, 30 ability power, 15 critical strike chance, 250 health, 250 mana, 12 movement speed. UNIQUE Passive: 25% chance on hit to slow the target by 35% for 2.5 seconds;on cast, increases your base attack damage by 150% for one attack Personally i think all should have Trinity Force, no duscusions there, besides it increases your amount of mana

Infinity Edge

75 Attack Damage, 20 Critical Strike Chance. UNIQUE Passive: Critical Hits now deal 250% instead of 200%. The damage this item gives is way to big to miss out on Ashe. Its a must to have this item.

The BloodThirster

60 attacke damage, 25 life steal. Passive: Gain an additional 1 Physical damage and 0.25 lifesteal per kill. Maximum of +40 damage and 10% lifesteal. Bonuses are lost upon death.I would personally go with this you can also go with Last whisperer for extra armour penetration

Greater Mark of Desolation

Armour Penetration is great if your team wants to gank a Tank. Armour Penetration is great overall.

Greater Seal of Clarity

Mana regeneration is one of Ashe's weakness so Seal of Clarity is necessary

Greater Glyph of Clarity

With glyphs of Clarity you will be shure to be able to spam volley without looking out for your mana. But it's just optional, I use it and you dont need more on glyphs.

Greater Quintessence of Desolation

Armour Penetration Ftw !

Ghost is great for helping teammates quickly, flee from gangking and chase badly wounded champions

I personally love heal, it helps alot in the begining of the game to get the advantage above the other champs. So it's optional.

Best survival spell for Ashe. This is your get out of jail free card if you make a poor positioning choice. It's also good for chasing if the situation calls for it.