Well, to get an idea of a similar space, you can look at what I'm doing in 10'x13'x11' here.
I never really went through the tutorials because I had previous software experience with XTrkCAD and RR-Track. But if I were starting from scratch, I'd start with Tutorial 01 and go from there. You can also go to YouTube and just search for "SCARM" and view the ones that interest you.
Once you're familiar with the commands, you need to decide how you want to use the space. If you decide to use a horseshoe like in the example I posted, you'll need to modify it. As it is now, you'll have problems reaching a lot of tracks. It's common practice to limit the distance you have to reach to 30"-36", so it would have to be more like the enclosed photo.
The biggest problem I see is the limited track selection, so it's really important to work with the American Flyer track library. As you can see, I added some turnouts, but with only 2 sizes to choose from, there are only so many configurations that will work and even these don't completely join up, so you either have to cut custom lengths or hope there is enough flex for things to connect.
In any event, there are folks here who will help.
