Create a new custom Layout page Template which will be visible in back office for page cms

customLayoutPage.xml

<!-- local/Namespace/Module/etc/config.xml -->
<config>
    <global>
        <page>
            <layouts>
                <template_name translate="label" module="Namespace_Module"><!-- Example template_name : homepage -->
                    <label>Template_Label</label><!-- Example : Homepage -->
                    <template>path/template.phtml</template>
                    <layout_handle>handle_name</layout_handle> <!-- Example : namespace_homepage -->
                </template_name>
            </layouts>
        </page>
    </global>
    <!-- Here we need to update layout with our custom xml -->
    <frontend>
        <layout>
            <updates>
                <namespace_module module="Namespace_Module">
                    <file>namespace_module.xml</file>
                </Test_Page>
            </updates>
        </layout>
    </frontend>
</config>

namespace_module.xml

<!-- design/frontend/your_theme/default/layout/namespace_module.xml -->
<handle_name translate="label" module="namespace_module">
  <label>Template_Label</label>
   <!-- Root -->
        <reference name="root">
            <action method="setTemplate">
                <template>path/template.phtml</template>
            </action>
            <action method="setIsHandle">
                <applied>1</applied>
            </action>
        </reference>
        <!-- Do what you need -->
</handle_name>