title: Creating custom shipping method with options
body: <p>I need to create a custom shipping method for a company, which is some sort of agent for a bunch of actual carriers. So during the checkout process a customer should be able to see a list of carriers and prices depending on his location (delivery endpoint). The agent company provides the API for retrieving this kind of information, so I have to determine the best way for integrating the API into the checkout process and displaying the delivery options. I know I need to override some models, blocks and templates, but I don't know, where to start. Could you give me the right direction? Thank you.</p>