Oracle not able to add Default value in PL/SQL
Single quotes inside single quotes need to be duplicated: default '' '' not null

 CREATE OR REPLACE PROCEDURE CREATE_TABLE AS
  strTABLE_NAME varchar2(32);
BEGIN

  strTABLE_NAME := 'Inventory';
  execute immediate 'create table '|| strTABLE_NAME ||
                    ' (STORE VARCHAR2(4) DEFAULT '' '' NOT NULL)';

END CREATE_TABLE ;


See the manual for details and alternative ways of doing that:

Text Literals | docs.oracle.com