How To?!

Does anyone have a clue as to how to make one of these? i can not afford one at $350 and up...
i would like to upcycle some old t-shirts and sweaters to make one for my two year old.
She is obsessed with tutu's and wings and hats and robes right now, so i figure this will help.
If anyone knows of a how to out there for these coats, please, let a momma know!
The Etsy maker of these is: GreenOakCreations
Hope that helps a bit...
If i come up with one prior to anyone finding anything, i will be posting!