I believe that in your case Stuart, you will find that because your modification is of UPVC, it is not classed as a permanent structure, in the way that bricks and mortar are. It is also an offence against Turkish " Building Regulations " , (Yes, we are deep in oxymoron territory folks ), to "extend the "living area " as declared on Tapu " ??!!
Again, as I said before, it is a VERY grey area, AND one which could, no doubt prove to be, ; çok pahalı !!