I think I figured out what I did wrong when I made Julie Sahni's phulka tonight, but not the reason they did not puff. Our guests were running late, and I decided to go ahead and roll them out. There was then about an hour pause while we had drinks etc. Then I griddled them and one of the guests (who had done this before with us, on the same range) then did them over the flame sans pan. I had thought about it before I rolled them, but figured that without yeast, it should be okay. Why didn't it work? Thanks!
I roll out roti ahead of time all the time, but I cover them with a slightly dampened clean towel. I don't like to roast them over the open flame, although many people do. Make sure your roti aren't too thick -- thick rotis won't puff well. I use a clean tea towel, folded, to press the roti along the edges -- the pressing combined with the heat creates the puff. When it's fully puffed, I remove from the heat with my chamta (roti tongs).
Flip uncooked roti onto the tava (griddle). When the top looks a bit dry, flip.
Cook the seond side until it has nice dark brown spots. Flip again.
Start pressing the edges with the clean towel and it will start to puff. Rotate the roti as you press, so the roti is moving, not your towel.
When puffed, remove from heat.