Heat a cast iron skillet or griddle over high heat, until a drop of water sizzles when dropped on it. Spread the skillet with a thin layer of oil and place one roti circle in the pan. Cook for 1 minute, flip, and spread the cooked surface with a thin layer of oil. Turn the roti every few minutes until it is cooked and brown flecks appear, about 5 minutes. Remote the roti from the skillet; let it cool for 1 minute. Then pound it between the palms of the hands until it becomes supple. Keep it warm and moist by covering it with a towel while cooking the other 3 rotis.