Sorry i posted my last message before i saw you most recent reply.. You can infer to draw a line perpendicular to another in sketchup by hovering for a moment over the existing line. if you are just experimenting with sketchup it is not that obvious at first. Its cool of you to go out of your way to experiment with it though. Don't let me bug you with fancy feaures ... i'd rather settle for the layer system you are working on so ignore this request.

Cheers!