A well-made roti balloons on the griddle while naan stays flat and blistered. Both are wheat breads cooked at high heat, and the difference is entirely structural.
Puffing requires a sealed envelope
Rolling a roti evenly presses the dough into a thin sheet whose upper and lower surfaces are separate but joined at the edges, with a weak plane between them.
When the bread hits high heat, the water inside turns to steam. The steam cannot escape through the sealed surfaces, so pressure builds and forces the two layers apart.
The bread inflates into a sphere. Once it cools, the layers settle back together, which is why a puffed roti is two thin leaves rather than one thick one.
Even rolling is the whole technique
A roti with a thick patch will not puff, because heat reaches the interior unevenly and steam forms at different times in different places rather than all at once.
A tear anywhere in the surface vents the steam as it forms, and the bread stays flat. This is why rolling technique matters more than any ingredient in the dough.
Naan is built the opposite way
Naan dough is leavened, enriched with dairy or fat, and considerably wetter. Leavening creates gas pockets throughout the dough rather than a single clean plane between two layers.
Steam entering those existing pockets expands them into the irregular bubbles that characterize naan, and it escapes through the connected structure rather than accumulating.
The dough is also stretched by hand into an uneven thickness rather than rolled flat, which further prevents the uniform two-layer geometry a puff requires.
Heat has to be high and fast
Both breads need steam generated faster than it can diffuse out of the dough. A cool griddle dries the bread out gradually and produces a stiff, pale result with no lift.
Roti is often finished directly over a flame or pressed on the tawa specifically to deliver a burst of heat to one side and trigger the inflation.
Doing it on an American stove
A heavy cast iron tawa or skillet brought fully to temperature substitutes for the traditional pan. Electric ranges need longer preheating because they cannot deliver a fast burst on demand.
Where an open flame is unavailable, pressing the roti gently with a folded cloth encourages the layers to separate and produces the same puff without direct fire.