There's a timber merchant on the Saniye that sells marine ply. Sorry can't remember what they're called. You'll see it all stacked undercover at the front of the premises. The good quality ply is very expensive compared to the UK.
It's difficult to get pressure treated wood in the area, although not impossible. 99% of roofs are built with untreated, often wet or green wood. That's why most of them tend to sag or collapse over the years.