I'm not particularly good at learning to use various computer programs. I learned to use Microsoft Visio quite a few years ago and got good at it so I have tended to rely on it for all types of drawings. While it is great for many types of drawings, to draw a layout plan there are several programs available that are especially designed for this type of work.
In the past I had tried XTrakCAD and CAD rail but had trouble of getting the hang of either of them. Then one of my local N scale modeler friends suggested AnyRail and I found it to be much easier to learn to use.
This is a drawing I did showing the 10 foot section of the layout that will represent the east end of the modeled area. The program allows the user to set up what the minimum allowed track radius will be and then as the track is placed in the drawing it will show if and where the track is tighter than that minimum. I'm still just getting started with this but already I would recommend it for anyone looking for layout design software. It can be downloaded at http://www.anyrail.com. The free trail version can do small drawings and does not have any time limit.