Back to Basics and a request from HPmadness about drawing curves.
I'm using the free version of "Sketchup Make 2014", other versions may look slightly different.
Well lets start with a new page
Remove the scale figure and at that point I go into camera -> standard views -> Top
This gives me a plan view.
I then using the box tool create my "sheet of paper", by zooming in and out you'll be able to make the Box as bog or small as you want. I tend to work on a real scale so my boxes will be 1200-1600m on the Red axis and 800-100m on the Green Axis. (Blue axis is vertical - 3D)
Select the curve tool click and hold down the button ath the start of your curve, and whilst holding down move the curser to the end point of the curve. There will be a dotted straight line form between the points.
On releasing the button, move the mouse and you will see the curve increase of decrease away from the straight line. The measure of bulge at the centre point is shown bottom right of the screen.
At either end point you can add a straight line, likewise you can put the start of a curve at the endpoint of an existing straight line.
At this stage the most important thing is that you always see the "on the face" marker. That means that the curve is being drawn on the face you are looking at.