After Create on database trigger not working, help?

I am attempting to create an AFTER CREATE on database trigger to assign DML privileges to different schemas.

For the test I have 3 roles:  RoleNum1, RoleNum2, RoleNum3

create role RoleNum1;

Create role RoleNum2;

Create role RoleNum3;

I have multiple schemas in a database (In the test I am using only 2 schemas)

schemao1
schemao2

A procedure is called by the trigger to assign the DML permissions to the roles:

create or replace PROCEDURE execute_app_ddl (p_ddl IN VARCHAR2) IS
BEGIN
EXECUTE IMMEDIATE p_ddl;
EXCEPTION
           WHEN OTHERS THEN
                RAISE_APPLICATION_ERROR(-20000, p_ddl);
END execute_app_ddl;

create or replace TRIGGER SCHEMA_GRANT_Test1