Shadow Fiend(Nevermore in the original DotA) is a very good hard carry who can outcarry many heroes.There is a "Default" build for him who is quite boring in my opinion and that's why i brought you this more interesting build wich has been tested by me.It works verry well if you have some farm.
For this build you will get hard right-clicking DPS(Damage Per Second) items.
Starting with a set of Tangos and a Healing Salve will provide you enough regen for sitting in lane and the Iron Branches with the Silppers of Agility will provide you the survivabiliti/damage you need.(If you random you can buy an entire Wirth Band wich is better)
Early game,either if you are mid or on a side lane you should focus on farming.Rushing your boots(Power Treads or Phase Boots) and your Shadow blade will be your first priority.If you have a good support on your lane who has some disables(like Shadow Shaman/Lion/Cristal Mayden) you can try some kills but be carefull,you can't do much early game and you MUST NOT die.
Mid game,when you have your Boots and your Shadow Blade you can be more confident(especially if you have a lot of souls).Shadow Blade will always be your escape.(Be carefull and always check enemies inventories for invis detectoin like: Sentry Ward/Dust of Appearance/Gem of True Sight).Continue farming and get your Mask of Madness as fast as possible but be carefull when you activate it because it makes you more squishy.
Late game you will be a killing machine with that reduced armor on your enemies and that armor and attack speed incrased for you.You still need to be carefull not to be focused in team fights or not to be ganked because you are still kinda squishy.(altought you have armor from Assault Cuirass)
Shadowraze - This is a nuke wich is maxed pretty early in the "Default build".In this build you will skip it because you're a right-clicker.
Necromastery - Your main source of damage early on because as you get souls your damage will increase wich will make you farm better and easier.That's why you max it first.
Presence of the Dark Lord - This is a debuff aura wich decreses enemie's armor in a 900 aoe.It will be maxed out along with Necromastery because it will incrase your right-click damage.
Requiem of souls - As long as you have Shadow Blade you can land some "perfect ultimates" wich will drain enemie's life.
Hopefully you will like this guide and this build.It's STILL so it's not perfect :)