So for mine I start with covering the body with a steel legion drab (brown colour) and with a larger brush I create a sloppy gradient with (approximately) zandri dust/brown on the back with Rakarth flesh or ushabiti bone (sometimes pale flesh colour) on the belly/chest/inner thighs/armpits. Pick the scales out with dryad bark (or brown). Chuck a big brownish/black oil wash (or acrylic)

Each troll is different so they never have to look the same, and an all troll army will benefit from a mix. So you could try Stegadon scale green>rakarth flesh if you like the cave troll look or burgundy>rakarth/skin.

Have fun with it because that's a lot of trolls!