title: Flutter build IOS on root of my flutter app does not work
body: <p>Whenever I run this command from terminal: <strong>flutter build ios</strong> in the root of the project for my flutter app, I get back: </p>
  
  <blockquote>
    <p>Cannot find "xcodebuild". Xcode 9.0 or greater is required to develop for iOS.</p>
  </blockquote>
  
  <p>Encountered error while building for device.
  I have the lastest Xcode (Version 10.0).</p>
  
  <p>Flutter doctor: </p>
  
  <pre><code>[✓] Flutter (Channel beta, v0.8.2, on Mac OS X 10.13.6 17G65, locale en-GB)
      • Flutter version 0.8.2 at /Users/h/flutter
      • Framework revision 5ab9e70727 (2 weeks ago), 2018-09-07 12:33:05 -0700
      • Engine revision 58a1894a1c
      • Dart version 2.1.0-dev.3.1.flutter-760a9690c2
  
  [✓] Android toolchain - develop for Android devices (Android SDK 27.0.3)
      • Android SDK at /Users/h/Library/Android/sdk
      • Android NDK location not configured (optional; useful for native profiling support)
      • Platform android-27, build-tools 27.0.3
      • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
      • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)
      • All Android licenses accepted.
  
  [!] iOS toolchain - develop for iOS devices
      ✗ Xcode installation is incomplete; a full installation is necessary for iOS development.
        Download at: https://developer.apple.com/xcode/download/
        Or install Xcode via the App Store.
        Once installed, run:
          sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
      • ios-deploy 1.9.2
      • CocoaPods version 1.5.3
  
  [✓] Android Studio (version 3.1)
      • Android Studio at /Applications/Android Studio.app/Contents
      • Flutter plugin version 24.2.1
      • Dart plugin version 173.4700
      • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)
  
  [✓] Connected devices (1 available)
      • h iPhone • 77afb908fc6c490d3fca62cdde9a74ab4e45b4f0 • ios • iOS 11.4.1
  
  ! Doctor found issues in 1 category.
  </code></pre>
  
  <p>I assume the IOS issue is thrown as I am running Xcode from an external HD</p>