Hi ,
pls have a look at this
here is a procedure to alert the dba when a tablespace datafile is nearing its maxsize
would this work

create or replace procedure alrt_size (a out number(5))
is
begin
select sum(bytes) into a from dba_data_files;
if a:=90;
dbms_output.put_line('the datafile is nearing its maxsize');
fi
end;