The key to make ragi roti or ragi flour chapati soft and with long lasting softness, is to hydrate it nicely in boiling hot water before kneading. Also allowing the ragi flour to hydrate while it cools ensure long lasting rotis. Also adding ghee to the dough makes soft ragi roti. An additional thing that you can do is to smear the freshly cooked ragi roti with ghee and place in closed container like a hot case. This prolongs the softness and the rotis do not get hard on cooling.