I am looking to make some PBR materials and I don’t really know where to start. I have been analysing some of the materials that come with the engine but I am at a loss. Can anyone point me in the right direction?
The best site to start is the documentation: https://docs.unrealengine/latest/INT/Engine/Rendering/Materials/PhysicallyBased/index.html 
There are some great things to read here as well.
://www.marmoset.co/toolbag/learn