So I had seen some posts last year about a "Twice Around" setup. I watched, planned, watched some more, planned some more...but I finally built it and I am very happy with the result! I wanted to keep it fairly small, so I went for O-27 gauge (4.5 ft by 4 ft). I also wanted some switches so I went with some used 1121's. I isolated the track into 3 sections and used some leftover electrical switches (it allows for the needed "Trolley Stop").
Below is the AnyRail file. The gap in the left center was filled in from the leftover cut in the overlap just above it. The two "half curves" in the right show they don't connect but O-27 does not have nearly the tolerance it is constrained to in the software and it fits just fine. It can support 2 trains running on the inner and outer loop, but my family seems to prefer just letting the Trolley have the right of way to the whole layout.
Here is the "dry fit" in the garage. I used 2x2's and 1/8 board to keep it light and low. After I cut the holes and ran the wiring I covered it with a green bed sheet. I stapled the sheet and screwed down the track.
Here is the final product complete with porcelain houses for the Trolley to navigate. Since this picture was taken it has grown to quite the metropolis as a Lego City Advent Calendar is being built around it.
Hope you enjoy! Merry Christmas.