Hi d3, did you figure out what you need?

MoI does not currently have very much in the "direct manipulation" of faces type stuff, so you generally can't grab a face and pull it or rotate it around.

Instead you would probably want to produce your result by doing a Boolean - have a box that is extended somewhat to the side, and in the front view draw a line at the angle you need:



Now select the box and run Boolean Difference, and select the line as the cutting object. This will cut up the box into 2 pieces:



Select the piece that you don't need and delete it and you will get your result:



- Michael