I am very familiar with these kind of shingles, same things are pre-made and sold in construction shops. But because Cambodia has almost no islands and coastline, these are more commonly made from coconut fronds. Near the sea some people make them from mangrove fronds like you've shown. You can buy one shingle for around 10 cents USD in Cambodia.
Some people who have a bit of money combine a zinc roof with coconut frond shingles on top, as this helps with cooling and lessening the sound of the rain.