It is not that God does some portion of creation and you do some other portion. It's also not that God finished doing his portion on a Sunday ;-) and now for the rest of the week you get to do whatever the hell you like without Him. ;-)
However, if you think of co-creation in terms of you NOT being separate from God, in which you are aligned with, one with, a medium for, and a conduit of God, then you effectively create WITH God when you are carrying out God's will.
This means that you do not necessarily have a separate will which can co-create to do things which God would not do. You only get to co-create with God, by being WITH God, and that means extending the creative ideals that God expresses. Love, peace, joy etc.
So yes you are co-creator because you EXTEND the Kingdom. But no, you are not co-creator who is on some kind of 'God team' who goes off by himself and calls the shots.
That said, there is perfect freedom in your union with God, and you are free to create anything with God, using God's power, which he shares with you on purpose to allow you to do this, provided your creations are in service and are aligned with God's laws.