General Opposites:
* Large
* Big
* Huge
* Giant
* Massive
* Enormous
* Immense
* Colossal
* Vast
More Specific Opposites:
* Expansive (referring to size or scope)
* Monumental (referring to size or importance)
* Grand (referring to size or magnificence)
* Broad (referring to width)
* Wide (referring to width)
* Tall (referring to height)
* Long (referring to length)
The best opposite for "tiny" depends on the specific context of your sentence.