Carbs, protein and fat are known as macronutrients, which means our body needs them in large quantities to carry out different functions in the body. First of all, you need to finalise your daily carb intake. On the basis of that you can decide how many chapatis you can have in a day.
A small 6-inch chapati contains around 71 calories. So, if your lunchtime calorie intake is 300 calories, you can have two chapatis that will be 140 calories and the remaining can come from vegetables and salad that you eat with the chapatis. Remember that not only chapatis, but even the vegetables and fruits you consume also contain some amount of carbs.
In short, how many wheat rotis can you consume in a day actually depends on your calorie intake. Having 4 chapatis in a day is considered optimal for weight loss.