It is past time for an update here. I did get started with construction this month. First I tore out an old 10 x 4 workbench at my mother-in-law's basement, and brought all the parts over here. Here is an inventory of the major parts.
2 rolling ends on casters that I left intact, built of 2 x 4s with 1/4" plywood as sides
4 10x1 x 8’ boards to be ripped into 1x4s and 1x3s
4 8x1 x 3’ boards
2 10x4 sheets of ½” Homasote
1 8x3 sheet of Masonite – no holes
2 2x4 x 10’
2 2x4 x 3’
1 8x3 sheet of ¼” plywood
I built a rolling base of the two sides, replacing the casters with new locking 3" casters. The purpose of making it rolling is that I will make it removable from the long narrower shelf so I can swing it out and get behind it for access. No need for pop up access now.
As you can see Unfortunately, it is not as high as I want to be able to look through the window onto the layout height from the laundry room. The window sill is 45" above the floor. I debated whether to make the roll around base higher, but decided to put in joists running parallel to the brick wall, and then put in perpendicular stringers. On the other side where I will have to build the whole thing from scratch, I will make the rolling base higher.
Anyway, here is the whole support with sections of particle board I salvaged from an old book case just laying uncut on top to get an idea of what it will look like.
The blue tape on the floor is roughly where the edges of the layout will fall. I know this isn't pretty, but I am a below average carpenter, using free wood, and once it is painted, track and scenery is on top, and a facia and covering to the floor is installed, no one will know the difference. What matters to me is that it is level, solid, but rolls freely when I unlock the four casters. 
I'll post more what I was going to write later. I just got a call to go see my aunt in the personal care home.
