Simplest Horizontal Geometry Question Ever

I'm embarrassed to ask this, but I think I've hit a wall.  

I'm trying to build a complex element (a building) with several odd angles. I'm using individual lines created using the "Line Between Points" tool.  Each new line is snapped the the endpoint of the line before it.  I want the angle of the new line to be related to the angle of the line it's snapped to so that when I move or rotate the original line, the angle between the two lines is maintained.  I've tried using Civil AccuDraw, but I can't figure out the right command or combination of commands to make it work.  Surely I'm missing something obvious... does anyone have any suggestions?

Thanks for your help!

Matt