I built Main Engineering tonight. One more deck to go (and a small one at that), and I can start framing the hull.
First, the profile:
Then the standard forward and aft perspectives:
The forward Turbolift is where it is because the forward edge of the neck is immediately above that shaft. I have no choice but to route the lift tube through the neck ahead of the Vertical Intermix Chamber (reference the discussion in the Tech forum). There is precious little space on O-deck that is available for full-height compartments (actually, Main Engineering is a 20% taller than the other decks in the secondary hull). The lifts route around Main Engineering, with a station dead-aft with access to a partial-height deck down to the control room above the doors to the shuttle bay. Dorsal Secondary Phasers are also located in this space.
and a tighter shot to get the horizontal intermix chamber:
As I finish these decks, I feel more and more like this is a real structure I am working with. Far more real to me now than pouring over all the 2-d plans in the world.
Once I frame the hull, I will have the proper limitations on the outer edges of compartments and structures, and will trim the protruding decks accordingly. Some of the "crawl spaces" I have not even begun to mess with, as I don't really know how much space I'll have to work with.
The next deck actually is mostly "crawl space" with some interface into the neck, but will allow me to define the upper edge of the secondary hull.