Sage advice, Bruce. I think the large scale segment of our hobby (obsession?) would profit from scratchbuilding. It’s challenging (but not too much) and it gives you an incredible feeling of accomplishment, not to mention some atta-boys from the gang.
As for plans, they’re great and I have borrowed a few (a hotel and my small cabin) from old Model Railroader issues. I’ve even drawn up plans of my own, after measuring and photographing actual structures. In some cases, I scale up plan view photos to 1:22.5 or 1:20.3 on a copy machine and with my scale ruler in hand, use them as measuring guides when I transfer these measurements to styrene sheet, my material of choice. I know that some articles suggest pasting the scale plans onto the actual styrene, but I find that messy, 'cause ya gotta peel all that stuff off.
Lately, I’ve been drawing up a rough plan just for reference sake and almost immediately transfering the dimensions to cardboard (for a mockup) and then to styrene–because I’m impatient.
Other than that, what you said.