Samle how to use variables in build.gradle

library_version.gradle

ext {
    support_version = '25.0.0'
    play_service_version = '11.0.0'
}

android {
  ...
}

dependencies {
  compile "com.android.support:appcompat-v7:${support_version}"
  compile "com.google.android.gms:play-services-location:${play_service_version}"
  ...
}