Wiring a string of lighted Railking buildings. Have questions.

From the descriptions that I've seen, the RailKing buildings will operate on AC or DC voltage. If you hook them up in parallel (the way you have them in your diagram) that should be fine. And as long as you're using AC from your transformer, the right and left power inputs should not make any difference.

I agree with Leo

Generally if one sees a red /black wire color combo it denotes polarity (probably DC voltage only - like LED lights). If one sees the same color wires or sometimes something like red/white, polarity should not matter but you need to check AC/DC or if both work. I have one MTH building. All internal wires are the same gray color. Red/Black wires exit from a terminal board. Whether or not this denotes polarity is required I don't don't since I have not applied voltage to the building as yet. My guess is polarity does not matter. Easy way to determine is to get a 12VDC wall wart (any wall wart you have for your cell phone or other stuff) and attach the wires to the building. See if the lights go on switching the wires around. If the lights go on both ways you have no polarity and both AC/DC voltage will work. If the lights go on in one configuration only (which I doubt with model train buildings) you have polarity and only DC will work.

Agree with Leo and Joe - plus, if you use an MTH 12 port or similar panel you can run your power wires to it and then run out from each port to each building and have 8 ports left for other accessories or future structures and have a nice, clean installation. They are available at most train stores and on-line and may be cheaper under a non-brand name.