It's best to go on the Saniye. There are several woodyards and there are also a couple of building suppliers there and on the Antalya Road close-by. (Try to get hold of an old pallet or 2 to use as a floor. That'll stop the wood standing in water and will keep the air circulating. )
Personally, I wouldn't bother with felt. It's a bit expensive. Go for heavyduty plastic which you can buy by the metre.