I could then suggest you have gridsnap off, and begin by holding down SHIFT and moving in the direction you wish to draw, … let go of the mouse (so you don’t move the rubberband,) and then release the SHIFT key and type the length followed by ENTER.
Other then that, I’m not really a LayOut person, don’t use it much myself.
So, you’'ll have to find some workflow that works for you.