In India, you would be able to walk into a regular grocery store and buy makki ka atta. Staying in London, I found it impossible to get hold of the main ingredient for this dish. So, after a lot of hit and trial, based on recipes that I found online, this is the concoction that has finally worked for me. I used a combination of coarse and fine cornmeal, and tried a variation with potatoes instead of radish.
Do not cook on medium or low heat as this will make the rotis too crisp. If you are using non-stick cookware, then oil is not necessary during cooking. Otherwise, dab the surface of the tawa and / or roti with vegetable oil during cooking.
The first couple of rotis are the hardest to make, but you will get the hang of it very quickly. Patience and some practice is all you need.
Usually 2-3 rotis per person will make for a good wholesome healthy meal.
You can replace mashed potatoes with grated radish, which is the more traditional way to cook this dish.
You can replace wheat flour with fine polenta (cornmeal) or gluten free plain flour.