This is just a test build at the moment. Any comments/ feedback/ suggestions would be nice. If its bad, explaining why it is bad would be greatly appreciated.

Ashe is a very squishy character and most of her damage depends from her items.

Masteries
21/0/9 would be a waste of mastery points and 9/0/21, im not used to but could possible work well for others, however i prefer the 14/0/16 because of the cd reduction of flash and the added movement speed. Having points on utility also means i do not need to waste runes on mp5.Having 14 points on offense helps me farm better because i am used to having Brute Force and Sunder because i played 21/0/9 before. This is a personal preference. The main thing is the 16 points on utility. Having the 3% movement speed, along with mercury treads and a zeal soon to be phantom dancer will give you about 400+ movement speed along with frost shot, which gives you immense kiting power.

Runes
9x on desolation because armor penetration is nice =D
9x on armor to help fend off against other ad carries early game/ and with 16 on utility masteries mana should not be much of a problem.
9x on magic resist per level to help against AP along with your banshees veil and mercury treads.
2x on Quints of Health for a bit of early game survival
1x on Quint of Desolation for just more armor pen

Other Choices for runes
9x Mp5 yellow, well some people may prefer this i usually find that if you use your mana wisely, with 16 on utilities you should not need this.
9x Cool down reduction, Ashe's cool downs are already pretty low, in my opinion this would be a waste.
2x quints of health? that depends on you if you want to switch it our for desolation then you can, but i prefer a bit more survivability than a bit more armor pen.

Frost Shot
Toggle on when hitting a champion, if you leave it on all the time it will drain all your mana.

Volly
This is where i disagree with some players. Volly, early game, is a skill used to harass players and not a skill used to be wasted on farming minions and spamming. If you time volly wisely it deals a ton of damage, don't let a volly go to waste, try to use it when you are almost guaranteed to hit them. Mid/ Late Game you can spam it all you want.

HawkShot
Don't underestimate hawkshot, this skill can make or break a team fight. Use it to scout the enemy or during lane phase use it to check the bushes for ganks, however you should be buying wards, so hawkshot should be used when you do not have a ward. Use it to check Dragon and Baron when necessary.

Enchanted Crystal Arrow
The magic arrow. This skill should be used to initiate, however i would be lying if i said i never used it as a sniping tool to KS( kill secure the enemy). It can also be shot at mid to help side lanes for ganks. This skill should almost always be shot right when its cd is over.

Flash
A skill that Ashe must have since she does has almost no means of escape. This skill can be used as a safety net for poor positioning of used to get a kill.

Ghost
Perfect for early game as Ashe is not very fast until she gets her mercs and zeal, used to escape from enemies also helpful for kiting/

Other Spells

Cleanse
Simply not as useful as Flash, it is not as flexible as Flash, since Flash can be used offensively and Defensively.

Teleport
I prefer ghost because of its survivability benefits compared to teleport. Ashe is very squishy and needs Ghost over Teleport.

Exhaust
As said above survivability is more important, let your other teammates get this.

Berserker's Greaves
Added 25% atk speed is nice but Ashe gets enough attack speed off her other items.

Boots of Swiftness
Slightly more movement speed is nice as Ashe is slow early game, however the 3% movement speed mastery makes up for this, so you can have a choice of better boots.

Mercury Treads
Added survivability is nice, with the tenacity maxed at 35 and +25 magic resist, not a bad deal since ashe does not get much magic resist from her items except banshees.

Why boots and 3 pots over doran's blade?
Boots and 3 pots helps survivability in lane phase. It can both allow you to play more aggressively or it can serve as a safety net if you get out harassed. There are 2 ways to play Ashe, which solely depends on the person you are laning against. Against a strong laner you most likely will be out harassed. If that happens try to avoid getting harassed as much as you can while mainly focus on farming because where you shine is mid and late game. If the person is a weak laner who is easily harassed by you you can deny him/her experience and it should be easy, while of course last hitting and farming. Conclusion: Harass or get harassed Farming is top priority. By the time you go back you should be able to afford 2 doran's blade for added survivability and either enough for your mercury treads or buy 3x pots and a ward.

If you have been farming correctly you should have enough to afford a Bf sword and then a zeal shortly after. With the Zeal, Merc Treads, and Bf Sword and 3% movement speed in utilities you should be able to kite almost anyone, you should also be beating out a lot of the other team's carries. Once you finish your infinity edge, there will be a significant difference in damage out put. Once you finish up Phantom Dancer you would basically feel as though you have ghost turned on 24/7. Team Fights should occur and you should be using your arrow to initiate and also it is extremely important to have GPS ( Godly Positioning Skills). A well positioned Ashe with good damage output can shred almost any team to pieces.

Last Whisperer v Black Cleaver
This depends on the team you are fighting. Heavy tanks go for Last Whisperer, If there are not much heavy tanks go for Black Cleaver. Black Cleaver is also more of a team item as it shreds armor benefits to your teamates when they attack them.

Starks Fervor?
I've been called a noob for using Stark's Fervor, but I personally like it because it gives me additional armor penetration, Life Steal and Attack speed which also benefits my team. Life Steal helps against those who have something like Thornmail and also it helps you recover after a teamfight to possibly have a team push.

Banshees Veil
I would like to say this is self explanatory, but Ashe's biggest weakness is that she drops if cc'd and Banshees prevents 1 cc every 30 seconds. It also gives her additional health and mana. What i normally do is sell Banshee's for guardian Angel when i have enough gold. By this time i would have enough gold to sell Guardian Angel everytime its on cooldown and purchase banshees and sell banshees when guardian angels cool down is up. Ashe is a game changing character and 1 revive my mean the win of a team fight.

Warding
Doing this ensures a bit more map control and it can prevent a death/gank so purchase around 1-2 wards every time you recall if possible.

GPS
1. Stay in the back or if you are in the front spamming volly try not to get caught/ cc'd
2. Focus down the other team's carries and NOT the tank.
3. This build has added survivability. With cdr on Flash and Ghost and 3% movement speed /Phantom Dancer and Mercs,and frost shot you should be able to achieve GPS and put other carries to shame.