This has been a great thread. I don't know if I should be envious or not of you that have such huge areas that you can use for your hobby. ON one hand, WOW. On the other, the sheer amount of work it will take for progress to be seen, let alone ever 'finishing it'!
My layout is 4 x 11.5'. It's quite literally at the end of a family room. Currently I have a 2x5 area cut out from the middle of it so that I can reach the far areas to work on it. Eventually those areas will be completed, and the open area replace with wood and then built on accordingly. It's essentially a double mainline. I am pretty satisfied with the overall space, BUT, the one thing I really really get frustrated with is the 4' limitation. In HO there is little you can do other than loop around-it won't accommodate any other plan. The outer loop uses 22" radius at the ends, the inner 18". I've petitioned for an extra foot or so at one end to allow for greater flexibility, but have repeatedly been denied.
However, I'm finding that the space is just large enough where I can model a good variety of things-'city' buildings, water/river, hills, trees, large boulders, etc.
SC