Thanks Mark for the separate topic on creeper idea. Lots of solid advice and experiences from members.
Here is the room dimensions that are final with the yellow area available for train layout. This is what I will be working with and need to maximize train/scenery area. I am inclined to follow your advice on doing track layout first and seeing where I will need to put decking. Sorry for the inaccurate measurements prior, as things were in a state of flux.