Build and Run of Android SDK - cannot select folder

Hello,

I am new to Unity but despite my lack of experience I decided to try and build an android VR application as my first project!

After creating the scene, I tried to build using the "Android-Support-for-Editor-2017.3.1f1". Once I selected "Build & Run", I was prompted to select a folder to save the apk file in. After I selected the folder it saves, which is fine.

The problem occurred when it prompted me to select an Android SDK root folder. Once I selected a folder (any folder) it just prompted me to select a folder again as if I didn't select a valid folder. The weird thing is that it didn't even tell me what was wrong. No dialogue box or error message popped up. The "select an Android SDK root folder" box just kept reappearing.

I have a feeling I missed something very obvious or that I didn't set-up a root folder somewhere I should have.

Any help would be hugely appreciated; this has stumped me.

Tom.