Build a simple App Xamarin

A product exchange application in which a user registers the products he has and what they need, these products are pre-registered and the app get the products list from our webapi and save this on memory, if on login have an update from products the app update the list saved. The system have a search engine must find another user who has the products that he needs through search parameters, through his location. This system would have the user's registration, association of desired products and products that it has, search engine and add contacts selecteds by result of search engine. This system has to communicate with a service rest web api, since the part of register is all the database the only thing that would stay in the app would be the data of locality and images/List of products.