There are a lot of options available to someone starting out. You'll notice that MR's project railroads have been a lot more flexible in recent years, even if they do rely on 4x8s to demonstrate basic techniques.
There is a lot of talk now about the "one-module approach" in which the builder creates one scene and gets it into operational shape before adding more segments and committing to a bigger project. Temporary staging boards with track and maybe a switch or two are used to move trains on and off the module.
Lance Mindheim's blog and articles give a lot of ideas on how to get some railroading going without getting overcommitted and overwhelmed.
Most big box stores have panel saws and will give one or two free cuts that can transform a 4x8 plywood sheet into 24 feet of 16" shelving for an around-the-walls design. I can get those into a VW Golf with a little effort.
Well, it's a chicken or the egg thing. There's lots of beginner plans for 4x8 and plywood comes in 4x8 sheets. Together they really encourage that size. But as you point out, an apartment isn't usually an option - although my first layout (4x8) was built in an apartment 2nd bedroom. (That lasted until our first child).
But once you have a basement or garage, you have the space. Roof racks will let you transport 4x8 sheets of plywood - I used removable ones on a VW bug years ago. But a lot of folks have small pickups or minivans which will allow you to transport 4x8's.
So I think the 4x8 is here to stay. If you built it on 4" wheels, you can roll it into a corner to cut down on the space it takes up.
If you have the room, I think building a 5'4" x 12' layout is a better option. It uses 2 sheets of plywood cut at 5'4", which can gives you 4 pieces that can be arranged into 5'4" by 12'. This allows larger radii and longer sidings. I have two 5'4"x12' layouts on wheels in my basement - one for Lionels with my grandson and one as a test layout.
Paul
I was wondering if most people entering the hobby today (in HO) build a 4x8 as their first layout?
The reason I am asking is
1. 4x8 sheets of plywood are getting more difficult to transport (cars getting smaller)
2. Home Depot (and possibly most lumberyards) will cut your 4x8 sheet of plywood either for free (Home Depot up to 5 cuts) or for a small fee.
I was putting the fascia on my old layout and I was able to get several 4x8 sheets of Masonite cut into 1' wide strips (I had to pay $1.00 for the extra two cuts).
I was reminded of this, and started thinking about that and its implications for the 4x8.
As cuyama has pointed out numerous times, and arround the walls type layout is a better utilization of space than a 4x8 (if you can fit a 4x8, you can fit a larger around the walls type layout).
The major drawback that I see is that your benchwork cost goes up significantly once you depart from the 4x8 layout (you need something to support all that additional plywood). You could use the walls as part of the support, but if you dont own the space, I can see this as being an issue. Making an around the walls free-standing is quite expensive.
Edit: I know because the last layout was built in an apartment, and I was not allowed to put holes in the walls for my layout, wife would not allow a large middle of room layout (she likes wide open spaces)(we live in New England.....)
Disclaimer: This is not knocking the 4x8, Im just curious if 4x8 is still the defacto standard.
My first layout that I called my own was an L shaped piece of plywood that was less than 4x8 (I want to say that it was a 4x6 sheet or something like that with a notch cut out of one side in N scale). The first Ho layout I had (shared with cousins) still exists and was a 4x8.