If you’re confused about this, you’re not alone. J. R. R. Tolkien ran into this little-known quirk of English grammar when he first began writing:
I first tried to write a story when I was about seven. It was about a dragon. . . . My mother said nothing about the dragon, but pointed out that one could not say “a green great dragon,” but had to say “a great green dragon.” I wondered why, and still do.
—J. R. R. Tolkien, The Letters of J. R. R. Tolkien
“Green great dragon” sounds as strange as “Greek, fat, big wedding.” Neither one works quite right. But why not?
The Elements of Eloquence: How to Turn the Perfect English Phrase
by Mark Forsyth:
[Adjectives] in English absolutely have to be in this order: opinion-size-age-shape-colour-origin-material-purpose Noun. So you can have a lovely little old rectangular green French silver whittling knife. But if you mess with that word order in the slightest you’ll sound like a maniac. It’s an odd thing that every English speaker uses that list, but almost none of us could write it out. And as size comes before colour, green great dragons can’t exist.
If you’re a native English speaker, you probably order your adjectives correctly without even thinking about it. This is a rule you didn’t know you knew.
It’s an obscure, seemingly insignificant rule. But as Forsyth points out, “green, great dragons can’t exist,” and neither can Greek, fat, big weddings.
from: How to Order Your Expressive, Long Adjectives Correctly
by Alice Sudlow