<FrameLayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:fitsSystemWindows="false"
    android:background="@drawable/back_blue_translucent"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <android.support.v4.widget.DrawerLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/drawer_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="false"
        tools:context="com.bentleycarr.mentalmaths.MainActivity">

        <FrameLayout
            android:id="@+id/container"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#f9f9f9"/>

        <fragment android:id="@+id/navigation_drawer"
            android:layout_width="@dimen/navigation_drawer_width"
            android:layout_height="match_parent"
            android:layout_gravity="start"
            android:layout_marginTop="72dp" <!--I want to change this -->
            android:name="com.bentleycarr.mentalmaths.NavigationDrawerFragment" />

    </android.support.v4.widget.DrawerLayout>
</FrameLayout>

Process: com.bentleycarr.mentalmaths, PID: 23729
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bentleycarr.mentalmaths/com.bentleycarr.mentalmaths.MainActivity}: java.lang.ClassCastException: android.support.v4.widget.DrawerLayout$LayoutParams cannot be cast to android.widget.FrameLayout$LayoutParams
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
        at android.app.ActivityThread.access$800(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5017)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.ClassCastException: android.support.v4.widget.DrawerLayout$LayoutParams cannot be cast to android.widget.FrameLayout$LayoutParams
        at com.bentleycarr.mentalmaths.MainActivity.onCreate(MainActivity.java:55)
        at android.app.Activity.performCreate(Activity.java:5231)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)

FrameLayout root = (FrameLayout) findViewById(R.id.yourID);
FrameLayout.LayoutParams params = (FrameLayout.LayoutParams)root.getLayoutParams();
   params.setMargins(left, top, right, bottom);
   root.setLayoutParams(params);

public class CustomMarginDrawerLayout extends DrawerLayout {
private static final int DRAWER_MARGIN_IN_DP = 48;
private final Context context;

public CustomMarginDrawerLayout(Context context) {
    super(context);
    this.context = context;
}

public CustomMarginDrawerLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
    this.context = context;
}

public CustomMarginDrawerLayout(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    this.context = context;
}

@Override
public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) {
    ViewGroup.LayoutParams params = super.generateLayoutParams(attrs);
    int margin = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, DRAWER_MARGIN_IN_DP, getResources().getDisplayMetrics());
    params.width = getScreenWidth(context) - margin;
    return params;
}

private int getScreenWidth(Context context) {
    WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    DisplayMetrics metrics = new DisplayMetrics();
    windowManager.getDefaultDisplay().getMetrics(metrics);
    return metrics.widthPixels;
}