My N-Scale model railroad is a freelance of the DT&I in the 1960s in Southeastern Ohio, perhaps around Jackson. The railroad is built on a 30" X 80" hollow core door with a 2" foam base. I obtained the design from Mike of Mike's Small Trackplans (http://www.cke1st.com/m_train2.htm). Mike graciously permits anyone to use his personal track plans, which are for N-Scale modelers. Visit Mike's web site as it's excellent and might even be life-changing for you.
I attached legs to the door on each end and drew my design on the foam as I laid out the railroad. I carved the creek bed and built the ascending grade. Then I laid the roadbed directly on the drawn design (I used cork) and then laid the track. After the glue was dry, I then scratch-built the portals to the tunnels and then built the mountain.
I began completing the scenicing, but that's a continual work. I would rather build and construct than run trains, but I'm a nut about having well-place track. Hence, I had to replace two switches (turn-outs) after the initial construction as I was not please with the lack of smoothness the trains would run through the first turn-outs.