Here's the N scale layout I purchased from my model railway club... it's a 30 year old, fully automated display layout that has been shown many times and won a number of awards here in Western Australia. It was largely built by friends of mine at the club (I was too young and inexperienced to be much help back then) and so is very special to me.
It's approx. 12' x 4' with a further 12' x 4' u-shaped shelf with staging yards for the 2 main lines. Up to 7 trains can run simultaneously on each mainline, and there's a mountain branchline on which up to 5 trains may be automatically passing one another and looping about. All done with old telephone exchange relays