CSX said:
ahh i was gonna tell you to go to thor trains. while a 3x9 is possible, i wouldn't reccomend it unless you try something smalle liek narrogauge, and old time 40' or smaller freight cars, or just trollies. you wouldn't be able to fit even a GP38-2, and barely a small switcher like an SW9. Steam is almost out of the question except for a few really small ones. you can have an industrial switching layout with like a GE 44 tonner, but thats about it.
i would reccomen a semi dogbone shaped layout, and just increase the ends just enough to fit an industry or a yard. the picture below is just a basic idea. you can add all sorts of things like a yard and such. some 6 axles road switchers ( i wouldn't suggest any bigger than and SD45) will be able to run on it, and it gives room for switching and such. depending on what kind of operation you want, you can decide the kinds of sideings and stuff you want. to add to it. this layout uses 18"r, which is good enough for most cars and stuff as long as you don't run long cars. its slightly wider than 3 feet, but only slightly. it fits in the 9 feet area. everything is either a 9 inch straight, or an 18"r curve, except for a 6 inch and 3/4s inch strack section at the top. i'll build more variations later.