I plan to build a directory web site by phpld, but there are not any content at most of the pages, can I add adsense at such directory site?
i don't see a point of adding adsense. who goes to directories? webmasters that who. do webmasters click on ads? not likely. never owned a directory,so i could be wrong,but i don't think i am.
yes, you can use adsense on your directories and i'm sure you can get so much money from your directory
I'd suggest you to choose another PPC program if you must, not AdSense, until it's fully established.