Ah. You problem is that by default, the model is rendered in perspective, but for your purposes you need "Parallel (also called orthogonal) Projection". Try this:
--In the CAMERA menu, select "Parallel Projection". This turns off perspective. The image will look funny to your eye, but it will turn off all the rendering adjustments that are causing your problems. For example, the parallel edges of a rectangle will always be the same size.
--Use the "orbit" tool to move the camera until you are looking straight toward the object you are interested. This is a little tricky--pay attention to the three axis lines.
You are now looking at a drawing just as it would be if drawn on a piece of paper. You can print it out and piece it together.
To be honest, there are tools that are probably better for your purpose, but all the ones I know are a LOT harder to learn, and SketchUp can do so many different things well that I still think it is your best bet.
