To build an NFT marketplace like Opensea, Rarible, or LooksRare with Bubble, start by registering for a free account and familiarizing yourself with Bubble's visual design tool and database fields. Design your user interface using Bubble's visual design tool, and then create the necessary pages for your marketplace, including a landing page, marketplace page, item page, connect page, and account page. Configure your database to store users, collections, and NFTs data, and then build workflows to connect these elements together. Use plugins like Rarible SDK and Pinata to handle minting, uploading media, and connecting wallets. Create a workflow for putting an NFT on sale, buying an NFT at a fixed price, and handling errors or rejections. Add additional features such as open auctions, timed auctions, search and filtering, and purchasing with fiat currency. Finally, set up privacy and security measures to protect user data, and consider hiring a developer or dev team to build your platform if needed.