Hi, i’ve been trying to make my model usable in UE4 for the last few days and i cant seem to do it.
I’ve found no documentation at all on what i should do to make a custom skeleton the most compatible with UE4. I have no idea how to add a root bone, and i have no idea on the right settings to use when exporting. Do i have to use the UE4 Mannequin skeleton? Can i use my own? If so, what should i do to make it work? Is there a way to make a custom model use the Mannequin skeleton?
And, i can’t stress this enough, how do i add a Root Bone???
Man, I’m having the same issue too 
Don’t add a root bone. Blender uses the Armature as the root when you export.
or rather, unreal interprets the armature object as the root bone.
You can watch some tuts on YouTube for my blender addon to get an idea of how things work.
Making a custom mesh is trivial after you know how the skeleton works and what a rig is supposed to look like.
http://mosthostla.com/gamedev/bonebreaker
The addon sets up your scene and the export axis/settings for you.
The learning process is literally trial and error.
You won’t find a tutorial showing you how because they are all pointless. Everyone does things differently. And every character’s needs are different, so it is to be expected.