rough idea
An approximate estimate or general conception (about something). There will of course be a lot more details when we get started for real, but these sketches should give you a rough idea of the design. I completed a similar program a few years ago, so I have a rough idea about what to expect.
*rough idea (about something)
and *rough idea (of something)a general idea; an estimate. (*Typically: get ~; have ~; give someone ~.) I need to get a rough idea of how many people will be there. I'll manage to get a rough idea. That's good enough.