My first module, build last fall, was a 72cm by 28cm straight section with a bridge. I used 9mm plywood for the frame and 22mm under the track. On this module I used Märklins c-track. The kit The sides are defined in a specification (guidelines). 12 mm holes spaced 5cm from bottom, 10 cm apart. in the center another hole 12 cm from bottom. The top 'cut out' is for the 22mm plywood carrying the rail (22mm * 60 mm). The bottom is for cables/wires. It is 30 * 60 mm. Preparing room for an Atlas girder plate bridge With the bridge in place Since I had no abutments laying around. Me and Evergreen took care of it. More work on the bridge abutments It seems to fit  time to add the good ole' Humbrol Filler Some pink foam glued in place using latex. (news)paper in place, We're ready for the plaster cloth.