The difference between plain roti and plain parathas is that parathas have oil in between their layers, and roti's don't.
Even after we put oil in the layers we still smear the front and back sides with oil while cooking them. That may be for taste though.
What purpose does oil in layers serve?
If we put the same amount of oil in flour while kneading the dough, instead of putting it in layers, will the effect be same?