I have got around to sorting the top level out, it will be 43cm wide for the entire length with a 120cm wide perninsula in the middle of the room. Once around that the line heads to the helix down to the lower level. The line up will join the top level on the left of the entry so I will need two lift sections (top and bottom levels) to get trains across the gap.
Due to the construction method there wont be many large geographical features on the top deck, I will leave that for the bottom deck where I have more room to play with. The track plan will be developed when I draw in the supports under the deck. I could have used more of the space for the layout but I wanted plenty of room for people to operate the layout.