As user "drab01"

CREATE TABLE DRAT_DDL_LOG 
(   DRAC_OPER VARCHAR2(30 BYTE), 
 DRAC_OBJ_OWNER VARCHAR2(30 BYTE), 
 DRAC_OBJ_NAME VARCHAR2(30 BYTE), 
 DRAC_SQL_TEXT CLOB, 
 DRAC_ORA_USER VARCHAR2(30 BYTE), 
 DRAC_USER_INFO VARCHAR2(255 BYTE), 
 DRAC_DATE DATE, 
 DRAC_STATUS CHAR(2 BYTE)
); 

create or replace package draddl IS
    function drag_schema_ddl
    (
        v_schema_name IN VARCHAR2
    ) RETURN CLOB;

    function drag_object_ddl
    (
        obj_name IN VARCHAR2,
        obj_type IN VARCHAR2,
        obj_owner IN VARCHAR2
    ) RETURN CLOB;
end draddl;
/

create or replace package body draddl IS
function drag_schema_ddl
(
v_schema_name IN VARCHAR2
) RETURN CLOB
IS
-- Define local variables.
n       NUMBER;         -- handle returned by OPEN
tn      NUMBER;         -- handle returned by ADD_TRANSFORM
doc     CLOB;           -- individual metadata for each object
ddl     CLOB;           -- Final ddl to be returned
BEGIN

-- Specify the object type.
 n := DBMS_METADATA.OPEN('SCHEMA_EXPORT');

 -- Use filters to specify the schema.
 DBMS_METADATA.SET_FILTER(n,'SCHEMA',v_schema_name);

 -- Request that the metadata be transformed into creation DDL.
 tn := DBMS_METADATA.ADD_TRANSFORM(n,'DDL');

 -- Fetch the objects.
 LOOP
   doc := DBMS_METADATA.FETCH_CLOB(n);

   -- When there are no more objects to be retrieved, FETCH_CLOB returns NULL.
   EXIT WHEN doc IS NULL;

   -- Store the metadata in the table.
   -- INSERT INTO drab01.my_metadata(md) VALUES (doc);
   -- COMMIT;
   ddl := ddl || ';' || doc;
 END LOOP;

 -- Release resources.
 DBMS_METADATA.CLOSE(n);
 RETURN ddl;
END; -- drag_schema_ddl

function drag_object_ddl
    (
        obj_name IN VARCHAR2,
        obj_type IN VARCHAR2,
        obj_owner IN VARCHAR2
    ) RETURN CLOB
IS
-- Define local variables.
n NUMBER; --handle returned by OPEN
tn NUMBER; -- handle returned by ADD_TRANSFORM
doc CLOB;
BEGIN

-- Specify the object type.
n := DBMS_METADATA.OPEN(obj_type);

-- Use filters to specify the particular object desired.
DBMS_METADATA.SET_FILTER(n,'SCHEMA',obj_owner);
DBMS_METADATA.SET_FILTER(n,'NAME',obj_name);

 -- Request that the metadata be transformed into creation DDL.
tn := DBMS_METADATA.ADD_TRANSFORM(n,'DDL');

 -- Fetch the object.
doc := DBMS_METADATA.FETCH_CLOB(n);

 -- Release resources.
DBMS_METADATA.CLOSE(n);
RETURN doc;
END drag_object_ddl;
END;
/
--- Now the trigger ---
create or replace TRIGGER DRAG_DUMP_DDL before DDL ON DATABASE
DECLARE
    stmt CLOB;
    old_ddl CLOB;
    sql_text ora_name_list_t;
    n pls_integer;
BEGIN

  IF ora_dict_obj_owner LIKE '___B__%'
       AND ora_dict_obj_owner NOT LIKE '%USER' THEN
        -- check if NBB owner or not
        n := ora_sql_txt(sql_text);
        FOR i IN 1 .. n
        LOOP
            -- put all statement lines in 1 field
            stmt := stmt || sql_text(i);
        END LOOP;

        CASE ora_sysevent --check type of event
        WHEN 'DROP' THEN
            -- on drop retrieve old DDL
            INSERT INTO drab01.drat_ddl_log
            SELECT 'DROP',
                    ora_dict_obj_owner,
                    ora_dict_obj_name,
                    stmt || ';' ||  drab01.draddl.drag_object_ddl(ora_dict_obj_name,ora_dict_obj_type,ora_dict_obj_owner),
                    USER,
                    sys_context('USERENV',   'OS_USER') || '-' || sys_context('USERENV',   'HOST'),
                    sysdate,
                    NULL
            FROM dual;
        WHEN 'ALTER' THEN
            -- on alter retrieve old DDL or skip message for compile
            IF(instr(UPPER(stmt),   'COMPILE')) = 0
                AND -- not a compile command
                (instr(stmt,   'BIN$')) = 0 -- not an automatic rename during drop
            THEN
                INSERT INTO drab01.drat_ddl_log
                SELECT ora_sysevent,
                   ora_dict_obj_owner,
                   ora_dict_obj_name,
                   stmt || ';' || drab01.draddl.drag_object_ddl(ora_dict_obj_name,ora_dict_obj_type,ora_dict_obj_owner),
                   USER,
                   sys_context('USERENV',   'OS_USER') || '-' || sys_context('USERENV',   'HOST'),
                   sysdate,
                   NULL
                FROM dual;
            end if;
  ELSE
    -- default case, log any command other then ANALYZE (truncate, create ...)
    if ora_sysevent <> 'ANALYZE' THEN
        INSERT INTO drab01.drat_ddl_log
        SELECT ora_sysevent,
               ora_dict_obj_owner,
               ora_dict_obj_name,
               stmt,
               USER,
               sys_context('USERENV',   'OS_USER') || '-' || sys_context('USERENV',   'HOST'),
               sysdate,
               NULL
        FROM dual;
    end if;
  END CASE;
END IF;
END drag_dump_ddl;
/
--- 
Now, still connected as user drab01 :

create table t5 (a number, b clob) tablespace USERS;

I get (from the drat_ddl_log):
"create table t5 (a number, b clob) tablespace USERS" in the drat_ddl_log.drac_sql_text 

For the alter statement:
alter table t5 add c CHAR(10);

I get (in drat_ddl_log.drac_sql_text column): 
alter table t5 add c CHAR(10);
CREATE TABLE "DRAB01"."T5" 
   ( "A" NUMBER, 
 "B" CLOB
   ) PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
  STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
  PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
  TABLESPACE "USERS" 
 LOB ("B") STORE AS (
  TABLESPACE "USERS" ENABLE STORAGE IN ROW CHUNK 8192 PCTVERSION 10
  NOCACHE LOGGING 
  STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
  PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)) 

But, when connected as user drab02 (with execute on drab01.draddl package privilege) 

create table test1 (x number);

I get (in drat_ddl_log.drac_sql_text column):
create table test1 (x number);

Then when I issue:
alter table test1 add y varchar2(10); 

I only get (in drat_ddl_log.drac_sql_text column):
alter table test1 add y varchar2(10)

ALTER TABLE <my_table> DROP PARTITION SYS_P146453;

create trigger can_not_drop_partition_trg
  before drop or alter on ea303v.schema
begin
  if ora_sysevent = 'ALTER' and ora_dict_obj_type = 'PARTITION'  then
          raise_application_error(-20001,'Cannot Drop partition');
   end if;
end;
/