Okay, that's a little better. I'd still like to hear more about what sort of railroad you want. It's nice to know that you'd like it to be three feet off the ground, but era, theme, region, etcetera are all things to consider.
The traditional pattern for model railroaders is the 4x8 sheet of plywood in the middle of the room. These are pretty easy to build, and there are roughly a billion 4x8 track plans out there (do a Google search for "4x8" and "model railroad", you'll get something like eleven thousand hits, many of which are 4x8 track plans of every sort.) There are some disadvantages, too, like sharp curves (the widest you can fit is a 22", which is fine if you like small locomotives, but can cramp your style if you like big steam or passenger cars) and limited mainline run.
Personally I'm an advocate (some might say 'fanatic') of shelf layouts, which are built around the perimeter of a room and generally not more than a foot or two thick. These require a little more handyman skill (but not much more than an island in the middle of the room) but have other advantages, like longer mainline run, broad curves, and the ability to build them in modular sections.
There are other sorts of track plan, too: you could build a "dog bone" layout with return loops at either end that narrow out in the middle along one wall, or even two walls, of the room.
An important factor is reach: generally, you'll want to have no point on the layout more than 30" from the edge of the table, and ideally less than two feet. For a 4x8 or other island style plan, it generally means having the table in the middle of the room rather than up against a wall, or having it on wheels so it can be rolled around. For a shelf layout, or anything up against a wall, it means keeping shelves relatively narrow. Fortunately, real railroads are very long, very narrow things, and model railroads can do this very well, aside from the odd return loop.