*Selecting a file to save too, plus inserting default file extension .xls
tables rlgrap.

DATA: ld_filename TYPE string,
     ld_path TYPE string,
     ld_fullpath TYPE string,
     ld_result TYPE i,
     gd_file TYPE c.

selection-screen begin of block m with frame.
   PARAMETERS: p_file TYPE  rlgrap-filename.
selection-screen end of block m.

* At selection screen
AT SELECTION-SCREEN ON VALUE-REQUEST FOR p_file.

* Display save dialog window
     CALL METHOD cl_gui_frontend_services=>file_save_dialog
       EXPORTING
*      window_title      = ' '
         default_extension = 'XLS'
         default_file_name = 'accountsdata'
         initial_directory = 'c:\temp\'
       CHANGING
         filename          = ld_filename
         path              = ld_path
         fullpath          = ld_fullpath
         user_action       = ld_result.
     p_file  = ld_fullpath.


source : http://www.sapdev.co.uk/file/file_objsave.htm