Why am I getting PLS-00103 when I try to create a table in a PL/SQL procedure?
You can not write DDL in PL/SQL block directly as you have shown in your question.

However you can execute these DDLs using EXECUTE IMMEDIATE command as demonstrated below.

  CREATE OR REPLACE PROCEDURE ddl_test AS
  BEGIN
  EXECUTE IMMEDIATE 'DROP TABLE tbl1';
  END;
  /