Welcome. This is my custom build for Fiddlesticks.

This build is based on getting maximum spell penetration and ability power to deal great damage. Moreover, spell vamp will enhance Fiddlesticks abilities (Drain overall) and gives you more survival.

Fiddlesticks style is to terrify enemies, lowering their magic resistance and dealing great damage with Dark Wind and Crowstorm. On ganks, Fiddlesticks can be very useful with Drain and, of course, Crowstorm.

Warning! When you complete this build your enemies will remember of your holy mother sometimes.

Enjoy it :)

As this build is about spell penetration, I pick red runes (marks) and quintessences to steal magic resistance from enemies, blue runes (glyphs) to enhance my ability power and yellow runes (seals) to get more health.

Spell penetration and ability power enhances the magic damage, while health gives your more "space" for draining enemies' life.

Following the spell penetration road, I pick all offensive masteries that can enhance my spell penetration and ability power. Also, I pick Cripple to enhance Exhaust, that will be very useful to extend your abilities and to escape from death and Sorcery that will reduce my cooldowns.

Then, I use remaining points with utility masteries, to enhance summoner's spells and mana and health regeneration.

Main items

Tear of Goddess: Will reduce the problems with mana in the early game.
Sorcerer Shoes: The must have movement enhancement and spell penetration.
Hextech Revolver: This is a newcomer item that can gets Fiddlesticks to a new level, as it will grant him 15% of spell vamp.
Rabadon's Deathcap: ABILITY POWER!
Abyssal Scepter: Additional ability power and some magic resistance. Moreover will help in lowering the enemies magic resistance.
Archangel's Staff: Additional mana, mana regen and ability power. Moreover, it gives additional ability power based on mana.
Void Staff: Additional ability power and magic penetration.
Will of Ancients: This will turns Fiddlesticks into a drain machine. Moreover, this will grant you allies 25% of spell vamp and will be great for magic damage ganks.

Attention! Archangel's Staff ability power is not beeing counted, so will get 2% of your mana in ability power, around 80 points.

My skill sequence is to get Dark Wind as fast as possible, followed by Drain and finally Terrify, as it effect's duration do not enhance substantially. Dark Wind is great at early game to hold the lane and keep the enemies alway. Drain is useful on ganks and to get attention on you, if you feel confortable to save your friends. Terrify duration increases in baby steps, so it's not a big deal to have it at level 5 in the early and mid game.

Obviously, I get Crowstorm always as possible, at levels 6, 11 and 16.

I pick Exhaust and Flash. Exhaust will extend your abilities duration and be very useful when escaping from death. Flash is useful to defend yourself, doing awesome wall flashes or running away and also to attack, ambushing enemies through wall and chase ready to death foes.

Champion selection

Line up with your team which lane you will take. Most of times mid will be a good lane for you, but some champs are big big trouble for Fiddlesticks, like Caitlyn and Morgana, in these scenarios, I would pick top or bot, soloing or in duo.

Early game

Level 1 to 6

Buy a Meki Pendant and two Healing Potions. Use Dark Wind to keep enemies away and to clean the minions. Now, I recommend you to do not clean the enemies minions all the way, let them pull a little so you do not have to push near enemy turret so early. Also, if you take mid, take care with ganks, mainly from junglers like Olaf and Warwick.

Mid game

Level 7 to 12

Now you have Crowstorm and it's time to start to terrify your enemies. Use the bushes to scare them with Terrify and Drain, but it's not time to be e dead hero, so go on baby steps. Line up with your team (mainly junglers) to gank the mid lane enemy and try to use Crowstorm to do not let them escape. I recommend you to use the mid brushes before casting yout ultimate.

Late game

Level 13 to 18

Now it's time to be more aggressive. After buying Abyssal Scepter, leave your lane (with caution, always) to kill enemies groups using your ultimate or to help on ganks using Terrify and Drain. Drain is ****ing awesome cause it really terrifies the enemies, most of times they will be confused between attacking and running away. Line up with your team assassins and then use Drain to attract enemies to you, while they getting killed.
After getting Will of Ancients, you will be the masterpiece on ganks, mainly with magic damage champs. Line up with your team and spread the terror through your enemies.

650g: To buy Tear of Goddess.
1100g: To buy Sorcerer Shoes.
1200g: To buy Hextech Revolver
3600g: To buy Rabaddon's Cap.
2650g: To buy Abyssal Scepter.
2855g: To buy Archangel's Staff
2295g: To buy Void's Staff
1665g: To buy Will of Ancients

Fiddlesticks is really fun to play. Keep in mind that he's somehow squishy (weak against damage dealers) and can be dead really fast when caught flat-flooted. It's all about positioning in League of Legends.

Always pay attention in how the game goes, sometimes will be necessary to adjust this build to win the game, and this that will make you a good player.

Any comments are welcome, thanks.