The problem with API 23 and Google Play Services is still not resolved.
Just in case you get something like “unable to compute hash of /intermediates/classes-proguard/release/classes.jar” – just add a few lines to the proguard-rules.pro.
-dontwarn org.apache.http.** -dontwarn android.net.http.AndroidHttpClient -dontwarn com.google.android.gms.** -dontwarn com.android.volley.toolbox.**
Stack overflow thread: http://stackoverflow.com/questions/30705589/gradle-build-failure
Star google bug: https://code.google.com/p/android-developer-preview/issues/detail?id=3001
//DL