Diva and grasshopper, question from a beginner

Hi, I just modeled a simple room with one window in Grasshopper, I'm not sure how to set up a 1"x1" grid to show daylighting results ? I've attached the file I set up. Also, I just started learning grasshopper and I need someone to check my work so far, I think I'm missing something, because the results aren't valid.

later I'll replace the ceiling with a more complicated one ( curvy ).