Create custom page layout in magento

In generally, page template is set under

<reference name="root">

For the set template, mostly using

<action method="setTemplate"><template>page/empty.phtml</template></action>

and Mark root page block that template is applied

<action method="setIsHandle"><applied>1</applied></action>

Suppose i am changing template   in checkout cart page :

<checkout_cart_index translate="label">
 <reference name="root">
<action method="setTemplate"><template>page/2columns-left.phtml</template></action>
 <!-- Mark root page block that template is applied -->
 <action method="setIsHandle"><applied>1</applied></action>
</reference>
 </checkout_cart_index>

  How to apply Custom page layout handles in layout in magento shwoing here..  

<custommodule_cms_index>
<!-- Custom page layout handles -->
<reference name="root">
<action method="setTemplate"><template>page/2columns-left.phtml</template></action>
 <!-- Mark root page block that template is applied -->
 <action method="setIsHandle"><applied>1</applied></action>
</reference>
</custommodule_cms_index>