Hi John I really like the layout plan. There are a few things that I would think about right off the bat.
1) I noticed that most of your layout table is 4' wide. I know that could be a problem for me, unless I had an overhead creeper.
2) if you removed the inner siding on the side where the TT is you could lessen the width down to around 36" which would leave you room for a service road!
3) I see you have a lot of O-32 curves. I know most of my engines are meant for 0-54 or bigger.
I also see the separation from the main table it only 4.75" I don't know anything that can go under that except an empty flat car.
I know one thing if we get a house with a room close to that size I will be asking permission to use some of your plan for my next layout!
Happy New Years!
