Please do understand that these are my personal preference when playing, this is not necessarily the best setup for you or for the champion in general. That being said I hope you find this page helpful ^^ The comnination of Sorcery and Domination give you bonus AP so your abilities do a little more damage early on when you are clearing.
Sorcery
Summon Aery Aery Is very useful in sustained fights. Although you don't gain much benefit from the shielding ability, you are able to proc this a lot in a fight dur to your semi-sustained damage nature.
Nimbus Cloak Fiddle's most powerful tool is his ultimate. Unfortunately it is only good when you can keep people inside the Area of Effect. This give you a nice burst of movement speed along with your passive which helps you close the gap and stick to targets.
Transcendence Despite Fiddle's need for CDR, many of his core items lack CDR as a stat. Transcendence helps with his because at 10 min you will gain 10% cdr for free. This allows you to path into more aggressive items earlier. Additionally if you do overcap on CDR you can gain even more AP.
Scorch Scorch can be a really nice poke tool early in the game, but once resistances apply the damage isn't actually too noticeable. Waterwalking and Gathering Storm are viable options but I personally am not a fan of them on him.
Domination
Zombie Ward Vision is a really important part of the game. Fiddlesticks is heavily reliant of abusing gaps in enemy vision to engage but also using your own vision to find opportunities to fight. Since you start of with a sweeping lens pretty early you can start getting some early vision when you clear out wards. It also allows you to track enemy movements so you can maybe catch them by surprise.
Ultimate Hunter A scarecrow is only as good as how scary he is. Fiddle's ult is the scariest thing about his so making sure you have it up as often as possible is very beneficial. Just make sure you use it when it is up.
Ingenious Hunter Reducing item active cooldown is sometimes underrated. For champs like fiddle, who engage fights, defensive tools can be the difference in late game teamfights. If you have a lot of item actives to use, this will reduce the CD on them significantly.
Bonus Stats
First Row: Take either Adaptive Force or the CDR. The CDR is nice if the game goes late but you shouldn't be in most cases.
Second Row: Take the Adaptive Force. More damage means faster jungler clears.
Third Row: Tank the 5 Armor or MR depending on the enemy team. You don't really lose HP in the jungle so the 5 armor is not a must. Don't take the HP.
Resolve Primary Alternative
It has become quite common that engage champs with high base damage and low tankiness to start taking aftershock as a primary keystone. This allows you to start fights and survive long enough to get off your damage and for your team to assist you. This is the Resolve primary tree I would recommend.
Aftershock On CC'ing an enemy you gain a substantial amount of Armor and Magic Resist for a short duration. This will enable you to engage fights and tank out a bit while sustaining yourself with your W ability.
Demolish Normally I wouldn't recommend demolish on champs that don't itemize towards HP. However, due to the slow auto attacks and low base damage fiddle can benefit greatly from this. When you successfully gank you can now push for turret plating with serious threat early on. This will allow you to grow your lead a bit faster.
Bone Plating When taking damage the next 3 auto attacks or spells on your deal less damage by a flat amount. This will increase your survivability in fights.
Revitalize This increases the healing you get back from your W ability. This allows you to take 1-2 point in it early and then to max it last.
Inspiration Primary
I don't recommend going for this if you are unfamiliar with your damage and playing as Fiddlesticks. This build works well when you understand your engage windows and abusing the lack of vision. Rather use a more standard build until you get used to how fiddle and his very unique playstyle.
Glacial Augment The slow on your auto attacks along with the freezing zone from item actives that slow make this a pretty useful keystone on fiddle. It allows you to have fantastic zone control, making it incredibly difficult for people to chase you or run from you.
Perfect Timing Basically the is the best option in this row for fiddle. You will build a zhonya's at some point in the game and having this in your inventory will either build into one or it can help you pull off some riskier plays earlier than your enemy will think.
Future's Market This allows you to purchase your core items a little faster and can really be useful when short a bit of gold.
Approach Velocity This works well in your build with your itemization towards slows. The MS is useful with sticking to targets and makes you very annoying to deal with.
