The spell animate objects lets a spellcaster animate 1 Small object per level, or a smaller number of larger objects. The spell description says that a Colossal object counts as 32 small objects for the purposes of this spell. Since a 20th level spellcaster only has a caster level of 20 (or maybe in the low 20s with magic items), it seems like it would be impossible to make a Colossal animated object before epic.
Is it possible for a spellcaster to use this spell to create a Colossal animated object before 21st level? How would you do it?
Any level of optimization is appropriate, though options that require less cost to a character (whether that cost is money, feat slots, class levels, or anything else) are better. For example, an answer that involves a prestige class wouldn't be as good as one that just used magic items. This can involve any level of resources that a character of up to 20th level would have access to.