Is there a way to create a Custom Field that is only visible by certain members or roles?
Welcome to the Forum @John_Altenbernd and thank you for reaching out!
As it stands, it is not posible to create Custom Field viewable only by specific roles but you can create Custom Fields for a specific Project.
You can create a Private Project, create those specific Custom Fields and add all members you would like to have access to those specific Custom Fields.
You can learn how to do so in this handy article: https://asana.com/guide/help/premium/custom-fields#gl-specific.
I hope this helps! Please let me know if you have any follow-up questions!