Sorry, I didn't catch what do you mean "how can I configure to create php.net error.log to all users for default on www_root"
In php.ini we have:
log_errors=On
...
error_log="C:\Program Files (x86)\Parallels\Plesk\admin\logs\php_error.log"
If you need debug log, you can enable it in registry:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\PLESK\PSA Config\Config
debug (REG_DWORD) = 1
In "admin\logs\" you will see debug logs like plesklog_debug20140115.log