Grenada Trader -- 2

I would like to make an app similar to OfferUp.com. I am looking to have both a web-based and mobile app that serves as a marketplace for the people living in Grenada. The user will be able to create an account and upload items that they can then sell to local buyers. If you look at Offerup.com as an example I would like the flow similar to that. The app would allow customers to post items for sale that a buyer can make an offer to purchase. The buy can pay in cash and or debit/credit.