I recently started a little game in 3D as an exercise (I'm way more comfortable in 2D), and right now it's best thought of as a 2D-in-3D (baby steps, here) shooter, with an increasing Y position moving things upwards on the screen and an increasing X moving things to the right.
But when I implement it, the value for DeltaRoll always seems to be 90 or -90
+90 & -90 are the pitchangle max min so it looks to me as if you're using the XZ axis rather than XY axis which you originally asked for.