flex extending a Mxml

Question

I have a complex layout and many reports need such a layout. Wondering if we can create a "template" like thing where every one can extend and get the layout.

Below is my first attempt.(this is just a dummy layout). The below has 3 canvas, one on top, one to left, one to right.

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
<mx:Canvas id="topCanvas" x="10" y="10" width="577" height="101">
</mx:Canvas>
<mx:Canvas id="leftCanvas" x="10" y="119" width="200" height="458">
</mx:Canvas>
<mx:Canvas id="rightCanvas"  x="218" y="119" width="369" height="458">
</mx:Canvas>

Question: How should I extend this to get reference of the "topcanvas" using mxml and add a button?