Here are two large layouts that belong in this design section. Both involve subways and elevated lines. One is my layout, the other I designed for a friend. My friend's layout also includes freight and Aurora slot car track. My layout is in the subways section and you can follow its progress there under topic NYC Subway Layout v2.0. I would like to stick to the design topic since I would like to leave this thread in this section and not have it moved to the subways section, albeit there is some non-subway stuff here.
First is my bi-level layout whose dimensions are 23x12x18. Here is the track plan and some 3D renderings.
My friend's layout will be HUGE, 26x45. It is also a bi-level layout that includes Aurora slot car track as well as freight. He wanted to have a mini-Queensboro Bridge for subway trains and a lift bridge for freight crossing a waterway with subway trains also running under the "river" as well as a vehicular tunnel using the Aurora track. Here is the track plan with sone 3D renderings.