conceptual work before starting dbt project

Hello everybody,
I would like to ask for best practices/ experiences to a possible approach to the conceptual work(this is at least how I would call the high level planning part). Following an explanation what I mean by that:

I am currently doing a dbt course and this is how I approach dbt modelling.
My thought process starts with: What kind of data do I want to provide to the enduser?
After deciding on that I am trying to come up with all the needed changes in my head and split them into staging/ int/fact_dim
This is way too much complexity to do it just in the head and I would like to start with some kind of UML diagram or something to do the conceptual work before I start the actual coding.

How do you do this conceptual part?