I would highly advise that this procedure be done as you are building the layout framework. I built a large three rail layout using the L girder framework method with a 1/2 inch plywood deck. All vertical wood strip board, L shaped grider, T shaped girder or plywood sheet butt type attachments that are attached to the bottom face of the plywood deck should be accurately measured and drawn on the top surface of the plywood deck. I use Circuitron Tortouse machines that are mounted to the underside of the deck sheet, using the marked top surface of the plywood deck, switches and switch machine can be located for no interference.
Tools needed tape measure, carpenters square, long straightedge and number 2 wood pencils, this may considered a timely process but it can minimize interference problems for as free hand or cad generated track plan.
