The alphabet goes from A-Z, but I go from Z-A. What am I?

There's nothing on draught when I show off my bars. Nothing hair to comb when I show off my locks. I can house rodents, I can house birds. I may be quite fancy or just the shape of a box.

I drift like cotton through the blue, changing shape as dreamers do. I appear soft to the sight but not to hold, I paint the sky in gray or gold.

From earth's embrace, I take my form, Molded by hands, soft and warm. With water's kiss, I find my way, To become art that shall not sway.

A sea giant's treasure, for your nose's pleasure.