Model railroading is a fun and fascinating hobby. Beyond simply running toy trains, model railroading lets you be the engineer, track designer, architect, and city planner. There are many facets to the hobby, providing an seemingly endless supply of different ways to enjoy model railroading. You might try using HO scale track to build this model railroad layout. At 1/87th scale, HO is small enough to build a nice looking layout on an old door. The smaller scales, N and Z, will give you much more room, while the larger scales, O and G, will be cramped for space.
Support the door so that it lies firmly, face up. Use the sawhorses to support the door, making sure they are the same height.
Use the straight-edged ruler to find the centre of the width of the door's face. Mark this centre mark near either end of the door. Mark the same distance in from the top and bottom of the door. There will be two resulting marks: each equidistant from the sides and end of the door.
Stick the pushpin into the equidistant mark and tie the string around it. Pull the string until it is one inch away from the edge of the door (use your ruler to make sure) and mark it. Hold a pencil against the mark on the string and draw a curve around the end of the door. Repeat this process for the other end.
Connect the ends of the two curves by drawing straight lines from one to the other, using the straightedge to help you.
Lay the model railroad track down along these lines, connecting the pieces together following the manufacturer's recommendations. The end result will resemble a large oval, with equally sized curves on either end.
Connect the power pack to the rails following the manufacturer's recommendations. Place the locomotive on the rails and test it.
Drive miniature spikes or small nails through the holes in the centre of the sleepers to hold it down -- don't glue the track down as it will be impossible to pull up if you want to make a change. The path of the track is called a track plan. There are many, many online resources to help you with your track plan and model railroad design and layout. Adding small details, such as bushes, trees, grass and buildings and roads will bring your model layout to life.