One design tool that is available is the Märklin track planning template (0212), an orange plastic pattern of all of the Märklin track elements.

Courtesy Märklin

The template allows you to draw out your layout to determine how much space it will occupy.  Or the template can be used to draw out a scale drawing of your available space to determine what sort of layout will fit within its confines. The template is scaled 1:5, which means that one cm on the drawing works out to be 5 cm of actual layout.

You will be using the metric system, so some mathematical conversion may be necessary. (This is especially true if you go to the lumberyard and ask for a piece of 122 cm x 244 cm plywood.  You won't get those bewildered looks if you ask for a 4' x 8' sheet). In any case, the template can be manipulated by turning it around, and upside down, to draw the necessary lines of track.

I have found it easiest to start with a curve in one corner of the layout.  If you are drawing a layout with the intention of determining its finished size later, draw out one corner, and extend the two lines that represent the edge of the layout some distance from that corner.  Then draw the initial curved segment. This forms a reference point for the layout, and the extended lines will help you keep the track lines in alignment.  You will notice on the template that the curved patterns are connected to lengths of straight track patterns. Use these to make sure that your straight track line is coming off the curves properly.  For turnouts, draw the straight track segment first, then follow with the curved segment. You may want to make a small mark perpendicular to the track center line as an aid for alignment of later sections of track.  In any case, the use of both a pencil and his buddy, Mr. Eraser, is preferable to pen and ink.

Once you are satisfied with your track plan, go back over the plan and clean up any rough lines and darken any light spots on the pencil tracings. Having done that, make several photocopies of the plan.  Now you can pencil in the different structures and scenery on an experimental basis. You may find it easier to cut out pieces from card stock that represent a scale model of the footprint of each of the buildings that you like. These pieces of card can then be positioned and the track layout manipulated until you find an appropriate place for each of them. Should you have chosen to design the track layout first, the pieces of card representing the structures can be placed around the track plan.  The other photocopies can be used for electrical wiring diagrams, and for roughing in the scenery.

You can take the scenery planning one step further by mounting a photocopy of the layout on a piece of cardboard or scrap plywood and using modeling clay to build mountains. This model of a model will give you a better idea of how the completed scenery will work out. You will find the photocopy machine to be very useful indeed.

One of the weaknesses of the track planning template is that you do have to exercise some care in laying out the tangent sections connected to the curved sections.  This problem can be overcome by using the Märklin Track Planning Game (0232). 

Courtesy Märklin

This set contains a fair number of miniature plastic pieces which represent the different track items manufactured by Märklin. While the track planning template is scaled 1:5, the planning game is scaled 1:2, which means that one centimeter on the game represents two centimeters of layout, so the resulting mockup will be much larger. The track pieces are really quite nice, featuring cast-in rails and crossties. Because they are designed to lock together, it quickly becomes apparent if things are misaligned. More importantly, these pieces lend themselves to repeated assembly and disassembly, something the real Z Gauge track will not tolerate.

The Track Planning Game is limited in that it has a specific number of track sections in it, while the track planning template is limited only by your supply of paper, pencil leads, and imagination.  The model of a model from the track planning game is more impressive and realistic, features that may be important to you. Once you have completed your layout planning, there are a couple of things that you can do with the track planning game. Märklin suggests that the pieces can be used to represent the layout on a control panel. In fact, some of the pieces have holes in them where light emitting diodes (LEDs) or small light bulbs could be installed. This would allow you to show the position of turnouts, whether a circuit is on or off, or if a track is occupied, depending on your skills and imagination.

Otherwise, you could use the track planning game pieces to represent a small industrial railroad, one that would serve a coal mine, steel mill, or factory. I will leave to your imagination the process of painting the colored game pieces, along with the construction of the various cars and tiny locomotives that would be used. Just imagine Zn30" Gauge trains. And you thought Z scale was small!