What brand of panel door motor can you get alex?
The reason I ask is because there are good ones and bad ones. The good are very good and the bad are a nightmare, I know this from experience I service/ install garage doors for a living.
Peter, If you have a heavy roof forget the bunnings panel motors, they aren't up to the load.
I have used panel motors successfully for 2 rooves and they work well.
Another more expensive option is gate motors like the observatory I automated here
http://www.gco.org.au/skylive/index.htm (scroll down to middle observatory). There are a lot more heavy duty and are not resticted to travel length like panel door motors, which is around 3m throw before you get into industrial motors (read expensive).
There are a few gate motors I can recommend to you, and a few panel motors I can recommend, and they aint the same brand!
Brett