Camillie,
There are variety of recipes for dosa. Simple recipe is using urad dal and raw rice. I use them in 1:2 composition.
1. Soak 1 cup urad dal and 2 cup raw rice (not parboiled) seperately over night.
2. Wash and Grind them in the morning to a paste consistency. Now mix both batters.
3. Leave it covered to fermentate so the batter expands to douple in size. It will take around 24 hours in a warm weather upto 36 hours in a winter month.
4.Once its fermentated add salt to taste and pinch of turmeric to the batter. If the batter is too thick add water and make it to pouring consistency.
5. Heat a large non stick pan. grease slightly with ghee/ butter /oil. When its hot enough pour 1 ladle full of batter in the pan and spread it in a circular shape. When the batter is cooke at the bottom turn it to the other side and cook.
Check this vedio: http://www.rakskitchen.net/2014/05/dosa-recipe-south-indian-dosa.html
You can make the idlis using 1:3 composition. But the batter needs to be thick and you need idly maker to steam the idlis.