trade application

i want to create an application with the same concept as olx or amazon or aliexpress but without any payment, only to show the diverse items that people want to trade locally and connect them with each other. Everyone can post an item and check other posts that might fit their needs and ask for a trade. the application will connect both of them with a chat log and contact details if they accepted the trade to communicate outside the app. And since the app is without payment, i need a space to add some ads . i wish if someone can help me with it with a low cost . i want it to work on ios and android. thanks in advance :)