The track bed is made from 12mm ply, glued and nailed into place. A pneumatic nail gun was a big effort saver, but by no means essential. The cutting operations took a lot longer. The ply has been cut at joins between modules; a lot of effort has gone into trying to get the joins level. The ply was be planed at the joints - just beware of splinters.
3mm cork sheet forms the final track bed. This is glued down under the areas where track will actually be located.
Finishing
I have put a fascia of "clean" timber around the front of the boards. This makes the railway more attractive, and covers the non planed timber. The edges are raised about 15mm above baseboard height, so that a derailed loco will have to clear a solid piece of wood before it can hit the floor.
There are shelves for boosters and booster transformers. There are hinged panels for the electronics (accessory decoders, block detectors etc). These things may not be strictly necessary - but remember this needs not only to be constructable but maintainable.