got Unity Pro 4.5.51f and downloaded Android SDK r23 (the latest one). After installing the SDK I tried to deploy to my Smasung Galaxy Tab 4. During build Unity asks me for the Android SDK root folder. By selecting it, Unity asks me again and again and again … Unity does not accept the Android SDK root folder …
I had this problem, too. This problem is at least three years old and it´s unbelievalble that it´s not fixed yet.
As far as I remember:
Uninstall the SDK.
Install it again but into a folder that you define (no standard installation).
Unity now can find it.
I know what I did wrong - my fault. By downloading and installing the SDK as-is is not enough. You have to install a few more packages through the manager - that should solve that problem!