how to give size to directory?

I want to save files to the folder like "D:\\Cache\\".. Before that I need to give size to the particular folder and save the files. So when the size is exceed it should show the message box like "The folder size is exceed, delete some files and save again".

How to do this.. i did the saving concept..

 

please anyone help me to assign the  size to the directory..

 

Thanks..