We've tried to satisfy the 90% case with the UI and "easy" options, especially those that transfer well from other push-to-build products.

To keep the UI simple and understandable for everyone, we decided to drop some options and require that you use a config for the more interesting cases.

There are lots of examples of config files (often named `cloudbuild.yaml`) in our github repo: https://github.com/googlecloudplatform/cloud-builders