Web Master:
Hey Anita, well a shadehouse's purpose is obviously to restrict direct sun onto the plants within, but my guess is that you want to also keep your plants warm. If this is the case then the sunny location would be a good choice providing that you have a double layer of shadecloth covering them. Many plants that don't like a lot of direct sun also like plenty of filtered light, so this may be a better way to go.
Alternatively if the eastern side of your house is sheltered (and you do live in Qld so it will stay warm) then that may also be a good location.
The key is keeping direct sun from your plants and then ensuring that the temperature within suits the type of plants you want to grow.