Hello,
VNTIS created good plugin, but in free version missing Interstitial Ads.
Here it is!
Version History
Last Update: 23.05.2015
ver 2.0 - google_play_services_version 7095000 Unity3d - ver 5.0
ver 1.0 - google_play_services_version 5089000 Unity3d - ver 4.6
Download
Download ver 1.0 from Here
Download ver 2.0 from Here
Source Code - tutorial
Here
This plugin is totally free!
BR