Ios – Flutter build IOS on root of the flutter app does not work

Whenever I run this command from terminal: flutter build ios in the root of the project for my flutter app, I get back:

Cannot find "xcodebuild". Xcode 9.0 or greater is required to develop for iOS.

Encountered error while building for device.
I have the lastest Xcode (Version 10.0).

Flutter doctor:

[✓] 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.

I assume the IOS issue is thrown as I am running Xcode from an external HD