This is a Google Deployment Manger (DM) template that deploys Couchbase Sync Gateway to Google Compute Engine (GCE) on Google Cloud Platform (GCP). simple is probably the best place to start.
marketplace is the wrapper code used in the Couchbase Cloud Launcher offers and probably best deployed directly from Cloud Launcher.
Documentation that covers deploying from Cloud Launcher as well as some best practices is available here.
Useful links are here.