I don't use accurate measurements but this is how I make it.
Take about 2 cups fine sooji and 1/2 cup maida or wheat flour, If you don't have fine sooji you can run the regular sooji in a dry grinder and make it fine powder.
mix a pinch of salt, 2 tsp oil and 1/2 cup or more water to make a soft dough. If it is too loose add more sooji or flour. Leave it aside for 10 - 15 mins so that sooji can absorb water. Wet your hands and knead the dough to make it pliable.
heat oil till very hot then reduce the flame to medium. meanwhile roll out a big roti and cut out small puris using a lid or a cookie cutter. drop the puris in oil, they should puff up immediately. Leave them in oil longer than the regular puris, till u feel they are crisp. medium flame helps here so they don't turn brown.
I keep them in the oven with the oven light on for an hour or two so they will stay crisp. after that store them in an air tight box.
I am still in trial and error phase though. Let me know if it worked for you.