WIKI: Workshop Syntax & Script Database - Workshop Discussion - Overwatch Forums (blizzard.com)
I don’t know if there’s a specific compiled Custom hero guide that is up to date because the Workshop has been updated fairly regularly with changes. However, there’s a few resources (such as the link above) that can help any new Workshop designer to try and find what they’re looking for to make a custom hero - and there’s loads of answered topics in the Workshop discussion that provide codes or answers for requested workshop ideas.
If you have any more specific questions just feel free to ask.