Pick a substitute based on the chapati texture you want: closest chew (whole wheat/atta-style) vs. softer roll (pastry/soft whole wheat) vs. quick emergency swaps (semolina or blended flours).
Use the table ratio for your starting amount of chapati flour.
Mix dough and check feel: if it cracks while rolling, add 1–2 teaspoon water per batch; if it feels sticky, rest 10 minutes and dust lightly with flour.
Knead briefly until smooth, then do a small test roll; adjust with a spoon of water (too dry) or a spoon of flour (too wet) before cooking the rest.