The larger the target object is, the more more powerful you must be to successfully cast invisiblity on it. This is true for all objects, whether they be people, rocks or houses.

A target must also be specified. Only the most powerful casters are able to cast an invisibility spell so powerful that objects are invisibile to everyone.

If a remove invisibility spell is not cast on an invisible object, the object will become visible by itself after a long enough period of time.