Use 'rough out' when you start planning something but aren't adding details yet. We should rough out our project plan today, then refine it tomorrow.
Pro Tip 2/3
Brainstorming stage
'Rough out' implies you're in the brainstorming stage, not the final stage. Let's rough out some ideas for the campaign and see which direction feels right.
Pro Tip 3/3
Not Binding
A plan 'roughed out' is not binding, and is expected to change as it develops. They roughed out a schedule, knowing it could be adjusted later on.