Welcome to my Ashe build.

This is the way I play Ashe most of the time. Ofcourse it always depends on the enemy team.

Have Fun reading!

Note: English isn't my first language

Marks: Armor Penetration

Arm Pen is just FTW, some people pick physical damage marks but they're worthless late game. It will be a little harder to survive and harras early game but as the game gets longer your damage will be nicer then someone with physical damage runes.

You can also choose attack damage runes for early game harras and the first blood. But i don't recommend these runes.

Seals: Mana Regen

Try to save a little mana early game. You can use volley to harras but not to much. Mid and Late game you can keep using volley the runes will provide you enough mana. When you're in a long teamfight you can end up without mana but this will rarely happen.

Glyph: Cooldown

Cooldown Glyphs will make it alot easier to harras. The cooldown on volley at level 18 will be +- 3 sec. The cooldown glyphs are great when enemy champions are chaising you. Because of the 3 sec cooldown on volley you can keep them slowed until you're safe.

Quintessence: Armor Penetration

Its just FTW for late game ^^

Masteries are quiet normal. 21 0 9, In utility the improved recall is a must. As a squishy champion it is really nice to escape as fast as you can. The 15% buff duration is also very nice it just rocks ^^!

In Offense just grab as many attack damage as you can.

Armor Penetration Marks.

Start with a DORAN'S BLADE. It is a must for early harras and some extra health. Some people start with Normal boots and 3 health pots but you won't do any damage and it is harder to last hit minions.

Try to stay in lane until you got 920 gold for Berserker Graves. (If the enemy champions play safe try to keep last hitting and gain 1650 more gold for a B.F sword. If you went back for your berserker graves frist then make your second back for the B.F sword.

After the B.F sword you will need some more movement speed and attack speed. So the next item is a Zeal (1195 gold). Try to stay in lane until you earned 1645 gold. With 1645 you can also buy your life steal (vampiric scepter). This will give you alot more surviveability!

The next item will be the infinity edge. It gives you a great boost in your critical damage and critical chance. You already got your B.F sword so will need 2180 more gold to compleet the infinity edge. This will be your 3th or 4th back.

After the infinity edge you will turn the zeal into a phantom dancer. The phantom dancer will provide you some nice attack speed, critical chance and movement speed. You will need 1650 gold to compleet the phantom dancer.

After the phantom dancer it is really team based. You can choose for a blood thirster if you are able to get some farm to benefit the unique passive. (+40 attack damage) It also gives some more life steal but you won't really need it because you already got an enormous damage output. And the 15% life steal from the blood thirster should be enough.

Another option is the black cleaver. You already got the phantom dancer so the stacks will add quickly! If you get the black cleaver you have to choose, leaving the last phantom dancer or sell your doran's blade.

And as final item another phantom dancer! 2 phantom dancers give you alot of attack speed, in combination with the infinity edge and black cleaver or bloodthirster you enemy will be down in a couple of seconds.

Physical Damage Marks.

Start with Normal boots and 3 health pots. because of your physical damage runes you got enough attack damage for last hitting minions and harrasing enemy champions.

TIP: Always stay at the back of the group fights, they will always focus you because of the massive damage and zero defence.

Flash: You're a squishy champion so flash is really a must to get away!

Ignite: Just for the extra damage at the end to pick up kills :) Ignite is just FTW ^^

Teleport: Teleport is also a very usefull skill.
TRICK: When you're on mid lane and the enemy champion is damaging your turret. Fire your ECA (Enchanted Crystal Arrow) in base and aim it on the enemy champion. Straight after u fired the ECA use teleport on the turret. You will be there on the same time as the enemy champion gets stunned!

Ghost: You already got flash but if it is hard for you to survive with flash only you can pick ghost too.

Exhaust: I never use it when I play ashe in my opinion it is useless. You got the slowing arrows to why do you want more slow? Just don't take it :)

Pros:

Great Harras
Nice damage output
Good chaser (slows & stuns)
Hot <3!

Cons:
Squishy
Slow at the start
No jungle
Hard to solo mana buff at low level (can't solo under lvl 10 w/o life steal)

Not the most detailed guide ever but if you got some questions or something just post them!