Brick co-ordinates change when I change the model viewing angle.

[Travis Cobbs]

If it's not flat when you right click in the view and select one of the standard views (left, right, top, etc.), then that means that you modeled it on a slope. So set the camera to one of the standard views, then figure out what rotations are required to get the model back in the proper orientation for that view, then repeat for the standard views of the other two axes. If you intentionally want the model to be diagonal, the better way to do that is to model it flat, then add it as a sub-model under the main model, and rotate the sub-model in the main model until it's at the desired orientation.