Some drawbacks of multi-level layouts...

[Green_Elite_Cab]

I saw one solution, in which the layout owner used a background that appears to continuously curve from the side to the "ceiling", in order to make the corner invisible in pictures. In theory, you could do something like this beneath the upper decks of your layout.

the only complication i can see is if you needed access to beneath the upper decks, but I'm sure there is a way to make this removable.