<resources>
 <item name="guide_percent" format="float" type="dimen">0.3</item>
</resources>

<resources>
     <item name="my_percent" format="float" type="dimen">0.7</item>
</resources>

<android.support.constraint.Guideline
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/guideline_vertical"
    android:orientation="vertical"
    app:layout_constraintGuide_percent="@dimen/my_percent" />