Keep your benchwork width and height about 3 feet and 3.5 feet.
An essential part of designing your model railroad is decision making and best belief. There are several choices to make when planning your model railroad. Do you want to freelance the railroad or copy a prototype? What kinds of equipment (locomotives and cars) do you want to run? You may want to add your own rules, like what you wish the layout’s height to be. How wide the aisles should be if you have aisles. You may want to make sure that all areas of the railroad have easy access. So you’re not having to break your back bending over or stand on a ladder or scaffolding to reach the farther sections of your track and scenery.
Most single layer model railroad layouts with backdrop are usually 3 to 3.5 in width. If you are building a layout you can access from both sides, make it no more than 6 feet deep so you can reach the center from both sides. If you are creating a two or more layer layout, make each section about 2 to 2.5 feet, so the structure does not get too deep, and you can reach each part.
On height, you do not want our layout base to go over 3.5 to 4 above the floor. If it gets too high, kids and short adults can see the first layer. But when it comes to each additional layer, you need it to be about 2 feet above the lower layer. The third layer would be about 8 feet above the floor. Most people will not be able to see anything. So most people do a cake layer design. Each layer should be set back 2-3 feet and only 1 foot up so you can get three to four-layer in eyesight.
If you are contracting a layout more than 4 feet in width, then you should place a spot where you can step without damaging the structure. Place extra support below the sites.
Remember that the benchwork width and height is your choice. Do not let anyone talk you out of what you want for your design.