for blog on databinding http://j2emanue.blogspot.ca/2016/01/android-databinding-big-picture.html

build.gradle

// Top-level build file where you can add 
//configuration options common to all sub-projects/modules.
buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.0.0-alpha5'
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}