I faced a similar issue making mitered half laps in 6x6s for an octagonal gazebo base. I have a pad full of sketches, note and drawings. I looked at Sketchup.
Being old-school, my solution was an easel pad from Staples with 1" grid lines on it, (Think of 25" x 30" graph paper.) I taped together 3 sheets and made a full size drawing of one side of the octagon base, including all the lap cut lines, post base outlines and mortise/tenon outlines. It really helped with my visualization, and got all of my dimensions nailed.