Homunculus is an improved familiar, it uses it's own stats where they are higher than the master's would grant it.
Personally, I think this is beyond the spirit of the rules, if not the letter, but I can see why someone would want to do it. The Homunculus starts with a crazy high strength for a tiny monster (8, when the recommended avg is 2 for tiny) and it'd also get stat boosts and size increases (which bring their own stat boosts) as you built it with higher numbers of HD.
Since it is tiny with 2 HD, and size increases are recommended in with every 50% increase of HD... you get to small at 3 HD (+4 Str, -2 Dex), Medium at 5 (assuming round up, +4 Str, -2 Dex), Large at 8 (+8 Str, -2 Dex, +2 Nat Armor), Huge at 12 (+8 Str, -2 Dex, +3 Nat Armor), Gargantuan at 18 (+8 Str, +4 Nat Armor). Each of those Str increases stacks. This means you Large Homunculus has a base Str of 24.
Furthermore, as a construct, it would get size based bonus to Hp, which would almost certainly push it above half the Hp of any average wizard.
That is some serious Cheese.