I don't know if you can do this already lexx, but here goes anyway to those that don't know....
To roll when you hit the ground:
Hold down crouch when you're in the air and hold down the directional key you wish to roll in. For example, I hold down crouch and forward and turn my mouse in the direction i wish to roll in (all in the air), then when I hit the ground, I'll roll instantly.
Someone please correct if this is wrong.