You can access Fester's hardware workshop by either tapping the tool kit icon at the bottom-right corner of the screen or go to the workshop itself which lies in'Fester's room'. Fester's hardware workshop will help you get the 'Expansion Materials' that are needed to expand to top-level zones. You can either complete the special orders for the asked for items to craft random growth products or you can save time and just acquire them with Addams coins.