Android Studio - Build variants not showing up

In your /gradle/gradle-wrapper.properties file update the following setting to:

distributionUrl=http\://services.gradle.org/distributions/gradle-1.8-all.zip

Now, go to Tools -> Android -> Sync Project with Gradle Files

This will download the latest distribution of Gradle and automatically reload your project and build variants after it's finished.

Make sure to update your project's build.gradle files to

dependencies {
    classpath 'com.android.tools.build:gradle:0.6.+'
}

You need to sync project with Gradle files:

In latest version of Android Studio: File -> Sync Project with Gradle Files.

In previous versions: Tools -> Android -> Sync Project with Gradle Files