as big as all outdoors
Very large. This phrase is typically used to describe expansive indoor spaces. After living in a studio apartment, my new place feels as big as all outdoors!
*big as all outdoors
Cliché very big, usually referring to an indoor space of some kind. (*Also: as ~.) You should see Bob's living room. It's as big as all outdoors! The new movie theater is as big as all outdoors.