Great post Andy, I can roll rounds and tear drops with my eyes closed but I am trying to think about how best to describe what I do.
If its chapattis I take off a piece of dough, roll it into a ball, i.e. round, then flatten the ball on the worktop, so it's still round. Take a rolling pin, roll away from you, turn the dough through 90 degrees, roll again, turn through 90 degrees etc until you have your desired size.
If still not happy you can cheat a little by putting a plate over your dough, run a knife round it - hey perfect circle. For a tear drop, do a circle, then pull one end away from you.
voila