Starter layouts are often flat and built on a 4 x 8 sheet of plywood. However, the majority of layouts have tracks at varying heights separated by grades. The easiest way to add elevation to a layout is to use open-grid benchwork. For this type of construction you place a plywood subroadbed under the track only and then attach risers to the grid to elevate that right-of-way.
Once the track levels are established, you then fill the open spaces between the levels with scenery.
A simple, sturdy way to support your layout is by gluing a 1 x 2 flange horizontally to a 1 x 4 vertical beam to form an L-shaped girder. The legs supporting the layout are attached to the beam, while the joists supporting the roadbed are attached to the flange. An L girder is very strong – the span between the legs can be as much as 13 feet. See fig. 5.