Rob,
If you have adequate space, you can always start small and add to any layout. In my opinion, that is the best way to build a large layout. If you build a layout similar to the last one shown by Larry, but you want to be able to bring in a longer train than you can actually work within the confines of the switching area, you could widen it slightly to add a single track main next to the switching section with a long run around. You could also make portable track extensions for one or both ends that can be set up during operating sessions and then taken down and stored with the layout between sessions.
As an insight into how much I like switching, I used to try to model an entire railroad in a small space where I could run trains continuously. Then I joined a modular club. I discovered that even if the layout we set up was 50 feet x 100 feet, after a couple of laps it was still trains just running in circles! Another member of the club built a module based on a modification of the "Gump Stump & East Snowshoe" from "101 Track Plans" from Kalmbach Publishing. I started doing switching on his module and found that I could spend hours switching out that layout without any sign of boredom.