Soga thatch is a fantastic roofing material, it provides great insulation, is entirely organic and if done properly will last a long time.
The thatch to the roof of this dining hall on Tavanipupu Resort in the Solomon Islands has lasted over 12 years and looks great. The essential element is to keep the thatching very tight and very close together when putting it in place, you will then enjoy a roof that is 95% waterproof. Anything that needs to be kept more waterproof than that, can be put in a cupboard.
When placed over the top of a sheet metal roof, thatch will sweat and rot, so that the next big breeze which comes along will blow it away. If done properly however, thatch will withstand most cyclones as the wind permeates through the thatch, effectively eliminating strong uplift forces.
But be aware the Soga palm endemic to Fiji is classified Endangered by the International Union for Conservation of Nature (IUCN), largely due to over exploitation by the resort industry.