I have used fine rava in this recipe. If you get roasted rava from the store, then you can skip the roasting part. Roasting the rava is an essential step if you don't want your idli to become hard and sticky. While roasting rava, you can add a teaspoon of ghee to give it a nice aroma. You can also substitute semolina with the same amount of idli rava, (similar to this idli recipe) if you looking for a gluten-free version.