Our second unit of the school year is entitled Dollars and Sense. It's a lot about different businesses. Last year I found this fun project by The Science Penguin that has kids design their own stores. It's mainly a math project, but it ties in perfectly with our first story which is called "Starting a Business".
The kids have to brainstorm their own business - complete with a store name and products, answering questions that tie in perfectly with learning about a business. They have to realistically think how they are going to set up the inside of their store (great perimeter and area lesson), and then figure out the outside of the building.
Highly recommend this if you need your kids to design their own store.