Any creature capable of taking Item Crafting feats can be of great assistance in the production of magical items. These feats typically require a Caster Level as a prerequisite, and Homunculi can be given any caster level desired via the Improved Homunculi option from the Alchemy Manual:
Spell-Like Ability: By incorporating 10 potions of the same spell in the homunculus’s creation, a crafter can imbue the homunculus with the power to use that spell once per day as a spell-like ability. Price: Total cost of the potions used.
Potions cost 50 gp * caster level * spell level, so by using a 0th level spell (which counts as 1/2 level) like Guidance, a Homunculus can be given an arbitrarily high caster level at the cost of 250 gp per level (or half that if you craft the potions yourself).
A Homunculus, as it has an intelligence score, also receives at least one feat. 2000 gp can be spent to grant it a second feat by giving it a third Hit Die, beyond which 4000 gp must be spent per feat.
Assuming you want to create Homunculi that assist you with the creation of Constructs you will need exceptionally powerfully homunculi possessing at least Craft Wondrous Item, Craft Magic Arms and Armor, and Craft Construct-- 7050gp in construction costs for the feats alone. Said Homunculus would also need CL 5 , which would cost 1250 gp for 8300 gp total (or 16600 gp to purchase).
Once completed such a homunculus possesses 5 HD, entitling it to an Ability Score Improvement, and can possess 2 skills at 5 ranks, which is good enough to grant it Craft and Spellcraft so as to be of use as an assistant.
It then can craft constructs on its own, provided some means of producing the needed spells (like you casting them), and can function as an exceedingly useful crafting companion.