Hello Kim
Yes, there are places to buy DIY materials. If you came down the mountain rd into Marmaris and turn right at the pearl roundabout then follow that rd until you get to the petrol station then do a u turn and go back on your self there are a couple of places. I think one is called Filla Boya there is also a hardware store in Icmeler and I am sure there are many other places that I don't know of. Having said all that I am surprised that you want to do DIY in Turkey. It is very cheap compared to the UK to hire trades people, I understand as low as £10 per day for labour and £20 for a trades man. We paid £400 to have a bathroom created in a hall way including tiling, plumbing, walls knocked down, brick wall built and electrics altered but not including the cost of the shower unit. I am a trades man here in the UK and know that there is no way I could justify trying to do the work myself but your time could be better-spent supervising Turkish labour. Best of luck with your project.

koctas in Bodrum, best to go to Izmir pratiker, koctas and ikea...
http://www.koctas.com.tr this is B and Q and rumours have it that they are opening a store in Marmaris soon.