Nice. That's pretty much what I was imagining! 
Imagination is a wonderful thing at times. 
I found this old thread on power to menards buildings from accessory side of transformer. Buck converters. How many leds will these service? 12 volts ac into 4.5 volts dc. I have a couple buildings that total around 50 or so lights. Do I need more than one? Also can they be used to supply a terminal barrier strip? Then wire buildings into that? Thx. TW
It depends on the specific converter. However, I doubt you'd be able to find any of the buck converters that couldn't power 50 LED's, so I suspect it's fine. 
Pretty much any of the eBay "buck converters" will easily service your 50 or so LEDs.
Yes, the output of the converter can feed a terminal barrier strip...which could then distribute pairs of wires (regulated 4.5V DC) to multiple buildings. The correctly sized plugs to the buildings with wires attached can be purchased on eBay for 50 cents or so.
As far as I know, Menards presently offers 2 adapters (1 and 3 output). The 1 output version has a rating of 1000 mA, the 3 output version has a rating of 2000 mA. As I have commented in several other threads, I do not recommend using these until they "fix" them to provide a regulated 4.5V DC output voltage as many guys have apparently toasted their buildings with their unregulated adapters.. Anyway, a simple rule of thumb would be to use 20 mA for each light. So the 1000 mA adapter would power some 50 LEDs. The 2000 mA adapter double that. If your buildings have blinking signs or the tiny motors that is another matter but you didn't mention that so no need to complicate the discusssion.
Virtually all the eBay "buck converters" will supply 1000 mA without issue so you're good to go for 50 LEDs. If you provide a specific link to an eBay "buck converter" one of us will confirm its suitability to your specific application.
Hmmm. Good news bad news. The lights are ok, but I bought the farm supply building and it has this leettle tiny fan.... Here's the one I am looking at. Came from the link above allbeit a few years old. Some are still available. Whadaya think? BTW, this whole thread was a great read!! Did Roger ever get his button pushed? TW.
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If the supply was set at 4.5 volts, there's no reason in the world that it would not run the fan.
It will run that fan just fine.
Mine does that and more.
You need to adjust the buck to 4.5 as John says.
However, the little fan has a plastic shaft on it which goes over top the motor shaft.
The fan is a really poor press fit and with mine the motor turned but not the fan.
I used a little Woodland's Hobby tack glue (the sticky stuff that stays sticky) on the shaft.
Enough to hold the fan on the motor shaft and yet removable if necessary.
Also did the following.............easy access and looks like someone is working on it.
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Thx for the help. Ordered three for $13.30, with shipping, be here by the end of april! TW. 
Another AC-to-DC converter option is shown below...save a buck or so when shipping considered. It also has screw-terminal blocks on input and output which may be of interest if soldering is not your favorite chore.
Could use the dollar-saved to attach a DC voltmeter module to your terminal strip to monitor the converter's DC output voltage. Note that when setting/monitoring the voltage you don't need to nail it at 4.50000 Volts! 4.3 to 4.7 is a suitable target range (within 5%).
Cables/connectors of all sorts and lengths - extension, splitters, un-soldered, soldered "pigtail" (wires attached), can be found on eBay for the plugs to the buildings. The magic search terms are 5.5 2.1mm which are the outside and inside diameters of the plug.
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What other applications can these buck converter devices be used for in the train environment. Further I have unused pc power bricks. 12v dc at 2 amps. Can these be used for anything?
There are countless applications in the train environment. Too many to list! The point is essentially all modern train electronics operates (or can operate) on DC voltage. But of course all O-gauge transformers and power sources only supply AC voltage. So your AC/DC converters can supply regulated DC power to virtually any modern accessory or even in rolling stock (for lighting, smoke units, etc.).
The 12V DC 2 Amp bricks equates to 24 Watts (= 12V x 2A) of power. Note that even the 3-output Menards power supply is "only" 4.5V DC at 2000 mA (2 Amps). That's 9 Watts (=4.5V x 2A). So one 12V paired up with two (or more) buck converters can provide the equivalent of two 3-output Menards adapters...and of course provide regulated DC voltage so as not to fry your buildings as is apparently the case with their current crop of unregulated DC output adapters.
This is a deadhorse I suppose, but why, with so many complaints, they don't choose to power with ac or at least regulate the dc voltage properly. Menards surely knows that the buildings are all over the layout, and to duplicate power for bricks is simply undesireable. DC must be cheaper. Woodland scenics sure gets it, 16-20VAC/Current: 75mA for most of their buildings.
