My layout is 13 x 13 feet and was designed and built for a very demanding set of requirements that basically amounted to ten gallons of stuff in a five-gallon bucket.
Here are the parameters:
-- Easy to build (my first layout)
-- Both Standard Gauge and 0 gauge
-- Wide radius curves to operate any and all available equipment (I also run at a museum that has a very large layout and most of my collection is geared to that environment. I wanted to be able at least to test run the big stuff, up to and including a 4-12-2 and a Cab Forward.)
-- One and preferably two wide-radius main lines to run two trains at a time, or to do test runs without taking everything else off.
-- One loop with sidings and postwar-style operating accessories.
-- Reasonable access to all portions of the layout as well as walls (display shelves, pictures, and one window) and the ceiling (skylight, ceiling fans, and light fixtures).
-- Access to the open center/control area through a hinged or removable section.
-- Provision to add a river and bridges later.
What I wound up with:
-- Essentially a square racetrack layout with four parallel tracks. The outer is 87" Standard Gauge, then 072, 063, and 042. Straights are 5' long. All track is tubular. There is a removable 18" wide section for access.Transformers are on a TV cart rolled under the layout. There is an open area in the center for controls and access.
-- All track is tubular. Hi-rail would have been nice, but I went with tubular for a couple or reasons. First, I had a lot of it anyway, including almost all the curves. Second, Standard Gauge just looks right on tubular, and I thought the layout would look better with all the same type of track. Third, I have a lot of ETS tinplate, which uses slider shoes instead of rollers. The square-edged center rail on hi-rail track chews up the shoes, which are expensive to replace since you have to get them from Prague.
-- The Standard Gauge, 072, and 063 lines are plain with no sidings.
-- The inner loop of 042 has three sidings - two dead-end and one passing. One siding has a Lionel coal ramp and diesel coal loader; the other has a barrel loader and a milk platform. The passing siding is quite short and is used for an engine servicing area with coal tower, water tank, and diesel fuel station. All switches are K-Line.
-- The inner loop also has an icing station, a piggyback platform, and a train order building on the main line.
-- All tracks have TMCC. The three 0 gauge tracks also are set up with DCS; I didn't bother with DCS on the Standard Gauge because I don't own any Standard Gauge locomotives with DCS. I do have a Lionel Hiawatha with TMCC, so I had to put TMCC on the Standard Gauge.
-- A 30" section of benchwork on one side can be removed and mounted lower to create a river valley to be bridged.
Tradeoffs, and things I would have liked but had to give up:
-- I could have done a loop of 072 with a passing siding instead of separate 063 and 072 loops. This would have given me more room for buildings and accessories. I might revisit this later.
-- I had wanted a tunnel. The four-abreast design and very tight space make it unlikely that I'll be able to do that, although I might squeeze in a short one in a corner.
-- I couldn't figure a good way to get in some grades or a second level, at least in the initial build. I'm still thinking about an upper level - maybe elevate the Standard Gauge to make more room on the main level.
-- I'd have liked to put in a line with bumpers at both ends to run a 50 Gang Car. No room. Ditto for a streetcar line, elevated or at grade.
-- There's not much room for buildings. A small passenger station and platform, a Lionel pedestrian overpass with speed readout, a couple of railroad buildings, and some Standard Gauge items in the corners are about all I have so far. I'll probably add a bar and a general store, but that will be about all.
On the whole, I'm pretty happy with what I've been able to cram into a small space. I'd post photos but unfortunately I had a computer crash and still need to do some data recovery. Will post when/if I can.