procedure privilege

I understand that in 10g and 11g, I can use the dbms_space.object_growth_trend to find out the projected growth and make capacity planning. But, this way can only go as far back as the snapshot allowed days. I created my own table and want to create the following procedure to run one the first day of every month so that I can query my table and find out info for how ever far back I want to.

create procedure collect_sizes
as begin
insert into my_datafile_info select trunc(sysdate), dba_data_files.* from dba_data_files;