In the below example I have created popup layout. In popup.activity layout, First I have created LinearLayout, In LinearLayout I added a TextViw and Button, then in step second I have created rounded.xml layout & in drawable folder, here I have also added dialog shape and color properties. You can see below program it will clearly describe you to create  how to create popup layout window in android

Step(1)-popup_activity.xml layout-

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="250dp"
    android:layout_margin="@dimen/margin_medium"
    android:background="@drawable/rounded_border"
    android:padding="@dimen/padding_small"
    android:layout_gravity="center"
    android:layout_height="110dp">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="@dimen/padding_small"
        android:gravity="center"
        android:textColor="@color/colorSpecialOffer"
        android:textSize="@dimen/text_medium"
        android:text="@string/maxSelectCat"/>
    <Button
        android:layout_width="80dp"
        android:layout_gravity="center"
        android:text="@string/ok"
        android:id="@+id/okButton"
        android:layout_marginTop="@dimen/margin_medium"
        android:textColor="@color/colorSpecialOffer"
        android:textSize="@dimen/text_large"
        android:background="@drawable/rounded_border"
        android:layout_height="30dp" />

</LinearLayout>

</RelativeLayout>

Step(2)-Create a rounded.xml layout in drawable folder

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
    <item>
        <shape android:shape="rectangle" >
            <solid android:color="@color/font_color" />
            <corners android:radius="12dip" />
            <stroke
                android:width="1dip"
                android:color="@color/colorPrimaryDark" />
        </shape>
    </item>
</layer-list>