In a large bowl, mix 1 cup barley flour, 1/2 cup rice flour, and 1/4 cup urad dal flour.
Add 1/2 teaspoon salt and mix well.
Gradually add water to the flour mixture, stirring continuously to form a smooth, lump-free batter. The consistency should be similar to regular dosa batter. Let the batter rest for 30 minutes.
Heat a non-stick tawa or dosa pan on medium flame. Once hot, pour a ladleful of batter onto the tawa and spread it evenly in a circular motion to form a thin dosa.
Drizzle 1 teaspoon oil around the edges of the dosa and cook until the bottom turns golden brown and crisp.
Flip the dosa and cook the other side for a minute.
Fold the dosa and transfer it to a serving plate. Repeat the process with the remaining batter.
Serve the barley dosa hot with coconut chutney, sambar, or any other accompaniment of your choice.