Some pipelines dealing with application code may to build deployment artifacts. The BuildStage can be used to accommodate this. Create a BuildStage then add it to your other linked stages in the appropriate position. Below is an example for building a deployment artifact which is later used to deploy to QA.
Let terraform-pipline know which build artifacts to save and make available using the saveArtifact method. Artifacts that match the pattern passed to saveArtifact will automatically be stashed after BuildStage, and unstashed in each subsequent TerraformEnvironmentStage.
// Jenkinsfile
...
def build = new BuildStage().saveArtifact('*/target/MyApp.war')
validate.then(build)
.then(deployQa) // MyApp.war will be available in the working directory
...