This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. The state or quality of being commodious.

n. State of being commodious; suitableness for its purpose; convenience; roominess.

n. The state or quality of being commodious; suitableness for its purpose; convenience; fitness: as, the commodiousness of a house.

n. spatial largeness and extensiveness (especially inside a building)

"Part of the "commodiousness" of a building should be how it serves people who may never enter it."

largeness    bigness   

seating capacity    airiness   

convenience    roominess   

ornateness    musicality    pertinency    miniaturization    sententiousness    wood-carver    pulchritude    wellspring    illuminator    somnambulism