I'm currently doing lesson 7 and I've had a dilemma with each of my drawings thus far where I can't tell if I'm "done" or not. I make the general construction and start going into the nitty gritty, but I hit a point where I'm not sure if it's worthwhile to include more of the details or if I should leave it as a more simplified version of the vehicle. Looking at lesson 7 submissions there seems to be a lot of variety in how far people go with their drawings.