Otto,
My layout will be over my wife's "layout" and the huge storage pace needed for mostly seasonal decorations. The Dept 56 display will have my Marx train and maybe a Thomas or Polar Express Lionel train run through it for the boys. The size and nature of the HO layout is heavily infulenced by the overall needs and wants of the entire family. Even the cats have to be taken into account. If you use the space under the layout for miscellaneous storage, be sure to protect any wiring, switch machines etc. Nothing more annoying than a perfectly operating railroad suddenly becoming a weekend troubleshooting project.