Well, I guess I'll go first- this is Chili's current set up...
Her cage stands 5 ft tall altogether, but the enclosure part is 28"H x 31"W x 23"D with 3/4" bar spacing (1" should be the max for Galahs). I would consider this size to be the minimum for a galah, but since I'm home pretty much all the time she's not confined to her cage for very long.
She also has her grapewood gym next to it, so she has somewhere else to hang out, and then also has a window perch on the adjacent window.
Inside her cage she has a big fat grapewood perch (which I need to rotate because she's ripped all of the bark off of it and has started making grooves in it with her beak lol) I also weave newspaper through the bars to give her some privacy on her top perch that extends the width of the cage (and it's also something for her to rip up).
She also has a pedi-perch in front of her main food bowl to maintain her little tootsies...and of course her boing since she sleeps on it.