Sift the flour and salt into a large bowl. Sprinkle over the oil, and add enough water to make a soft dough (about 140ml/4½fl oz) – add a little more flour or water if needed. Knead gently until smooth. Cover and leave to rest for about 30 minutes.
On a floured work surface, divide the dough into six equal pieces and roll each one into a thin circle about the thickness of a 20 pence coin (about 2mm), using a rolling pin.
Brush the bottom third of one of the roti with oil using a pastry brush, dust with a little extra flour and fold the oiled third towards the middle. Repeat with the top third, fold inwards again. Give the roti a quarter turn (90 degrees) and repeat the folding process – you should end up with a rough square. Leave to rest while you make the remaining five rotis.
Heat a little oil in a heavy-based pan. Using a rolling pin, roll out one of the roti thinly and then fry on one side until it puffs up and is speckled brown on the underside. Turn it over and fry on the other side for a few minutes, until it too is puffed and speckled brown. Remove from the pan, allowing the roti to cool for a few seconds, then fold into four. Wrap in a clean tea towel placed in a colander until ready to eat. Repeat until all the roti are cooked. Serve warm.