General Size:
* Huge: very large
* Vast: enormous in extent or size
* Immense: extremely large; vast
* Colossal: extremely large; gigantic
* Gigantic: very large
* Massive: very large and heavy
* Monumental: very large and impressive
* Enormous: extremely large
* Extensive: covering a large area
* Expansive: very large in area or scope
* Grand: impressive in size or scope
* Brobdingnagian: extremely large (humorous)
Size Relative to Other Things:
* Oversized: larger than usual
* Outsized: unusually large
* Bulky: large and heavy
* Voluminous: occupying much space
* Stout: thick and strong
* Imposing: large and impressive in appearance
* Dominating: large and powerful in appearance
* Preponderant: greater in number, amount, or importance
Descriptive Words:
* Spacious: having a lot of space
* Expansive: wide-ranging
* Broad: wide in extent
* Wide: extending far across
* Deep: extending far down
* Tall: high in height
* High: reaching a great height
Words for Specific Things:
* Imposing: large and impressive (buildings)
* Widespread: extending over a wide area (influence)
* Prolific: producing large amounts (writer)
* Abundant: existing in large quantities (resources)
The best word to use depends on the context and the specific effect you want to create.