How to setup Franchise account in commerce tools?

I have a requirement that in Commerce tools to setup an Franchise and map all their shops to that. Whats the best suggestion I can use ?. Can I go with Business unit and map all their shops how does that work

If you mean as a big company you want to sell within multiple web shops you may want to use stores for this.
That way you have one commercetools project key which has multiple stores (they can have different inventory and distribution channels with different product prices and locales). As an example you could have a store specific to selling products in the US with languages English and Spanish and prices maintained in USD (this is done via the product distribution channel specific prices) and another store for selling in the EU with prices in Euro and languages like English, Spanish, Italian, German, French...

If you have a big customer and want all orders for this customer to go through the same customer account but have different people with different rights to create orders within your web shop then business units might be the way to go. Example: you are selling to other big businesses and have a customer who orders your products in different countries but they are all under company name XYZ. Then you could create a business unit called company XYZ and have XYZ Ltd., XYZ LLC and XYZ GmbH as sub branches with associates assigned to each sub company with different roles to only buy or also administer the business unit.