With a high enough ride check, everything is a mount!
So, yes, you can ride it.
One thing to note, if you attempt to ride a creature that is ill suited as a mount, you take a –5 penalty on your Ride checks.
Also watch out for your homunculus' encumbrance.
Without knowing what you're using, I will assume it is a mauler-archetyped Homunculus with the winged 2-pt. evolution. A few of the normal familiars (of which a homunculus should resemble) are probably considered suitable for a mount for a size smaller PC. Worst case scenario, you didn't pick one of those.
-5 to all ride checks due to ill suited mount.
-5 to all ride checks due to a lack of saddle.
Your ride checks would use your normal skill modifier -10. The DCs listed under the ride skill don't change.
The most important skill there is probably "Fight with a combat-trained mount" DC10, and a free action to try.
Since your homunculus is intelligent, it should either qualify as "combat-trained" or should negate the need to make this check.
I recommend getting it a saddle to negate that second -5 to your checks.
what kind of ride check am i looking at? 20 30 40?
You use all the same DCs listed under the Ride skill, just as if you were riding a horse.
However, if your mount is not really made to be a mount, you take a -5 penalty on all of your Ride checks to do the things you could do on a more appropriate, mundane mount.