Flag Factory

To me they all look the same - the Union flag as we now have to call it (stupid Political Correctness...) features on both the Australian flag and the UK flag, and the George Cross is part of the Union flag. So I don't see how much you could change...

yeah the union flag is just made up of Scotland's Saint Andrew's cross, England's Saint George's Cross, and Ireland's Saint Patrick's cross

I think perhaps it would be better to go HERE and choose one of the basic designs that are about half way down the page under the subheading "basic patterns in flags."

Then, choose colours and other design aspects, keeping in mind the basic rules of flag design which can be found HERE.

EDIT: Regarding the flags above, two shades of green next to each other is vexillologically improper.