Almost every building in the Kaya Valley is illegal. Some are more illegal than others depending on the amount of grease slapped in someone's palm !
Apparently there will be an amnesty " sometime in the near future " for houses that have already been built and there will be " restricted" building allowed. Hence the number of plots of land that are currently having walls built around them and "Satilik / For Sale" signs put up. When the go ahead for "restricted building is given, the land value is likely to increase 10 fold.
By some quirk of Turkish law, my house is illegal, but by the current law, it will become legal on the day I die.
To be perfectly honest, I wouldn't touch any property in the valley until there is an official announcement.
However, if you want to invest purely in land in the valley for the future, now is the time to get on the bandwagon.
Or, have you considered renting? I understand that there are quite a few very nice properties to rent in the valley. Far better to try before you buy.