So with the understanding that benchwork construction in still months away, here is my current thinking on the layout.  For those keeping track, this is a change from what was posted earlier.

The sloping roof of the attic presents a challenge vertically at the outer edges of the room.  This forces the layout surface down low if one wants any sort of backdrop...  So in order to maximize the 14 foot width of the room, I've decided to take a seat - literally.

By committing to sitting down on rolling chairs, I can lower the base height to 28 inches and have 20 inches of backdrop on the outer walls of the layout.  The terrain will climb when it moves to the center of the room since there is plenty of room vertically there.  This will also allow room for hidden staging under the mountain section.

Note:  The image above is only the mainline portion of the layout...  I'm still working out staging and return loops.  You will also note that I've added "People" to the isleways to give a visual feel for the size of the layout.

I'm trying to keep the scenic depth to 30 inches max. and the isleways are also 30 inches wide.

By the way, for those who are curious the layout drawing is done with a program called AnyRail.  After trying almost all of the track planning cad software out there I settled on Anyrail for two reasons:  1.)  It is obviously current in its technology.  2.)  It is intuitive to use.