I think what you need to do is create two build configurations in TeamCity, one to build and one to deploy with Octopus. Refer to this link that has a small blurb toward the end:
Note that NuGet packages created from your build won't appear in TeamCity until after the build completes. This means you'll usually need to configure a secondary build configuration, and use a snapshot dependency and build trigger in TeamCity to run the deployment build configuration after the first build configuration completes.
So in my case I created 2 build configurations, then setup a snapshot dependency from the build to the deploy config and also a trigger to kick off the deploy after a successful build.