So Devon, I found out that styrene is the best bang for buck. I’m just going to use 1/8 and have more internal bracing. Cheaper to double up or even triple up 1/8" to get to the price point of more expensive thicker plastics.
Came home with 4x8 sheets of 1/8 (4x), .060 (2) and .040 (2). I still had enough .030 to last for a while.
In addition to my 3D modeling I have done some physical modeling. I have the first 1 1/2 layers of the main Hecla building cut out of foam. I ran out of it, dang thing will be huge. But I am using 1" thick pink foam to build up the layers of the main building which will be nothing more than a flat facade against the house. It will be two layers of foam to give the feel of the front of the building. I will get some pictures of it soon.
I have decided to use mostly Roosters technique. I am making it out of foam without any “cladding” I have decided to make it board and batten instead of tongue and groove. I will leave the foam as is and then glue on trim and battens made from styrene or printed details. Heeding Rooster’s comments, with the scale of this building the cost would have been outrageous to use some sort of plastic sheet materiel. So a base of foam then painted and adding styrene and printed details will look good and be coast effective.
Looks good so far. It is going to be bigly!!!
Go big or go… bigly!! 
FWIW Devon, when I made a similar-size foam model, stainless deck screws (and foam adhesive) worked really well for holding / clamping. And you can just leave them in.
I learned this trick from Winn Erdman, who’s made some spectacular and large structures having a foam substrate. An example:
https://www.mylargescale.com/threads/embudo-station.28232/page-2
Doesn’t foam even when properly covered degrade over time when exposed to the elements? I’ve kind of already committed to my feed mill being plastic but I might consider foam core for another large structure I need but I worry about long term stability, etc.
Craig I have seen where people leave them out, some over 5 years with no issues, I have 1 I’m making and will be covering the exterior with vinyl cement to simulate a concrete warehouse.
Pink foam is pretty resilient as long as UV doesn’t get to it. I’ve never put it to the test in a fine scale model but I think if painted and minor up keep it should protect it for years.
And given the expansive nature of this complex cost is a factod
As to it being “bigly,” its almost 5feet wide
Umm my feed mill is 6x7… 
So yah I know it adds up fast.
Cliff,
That thread looks like a good one at first glance. Very much in keeping with how I was thinking of proceeding. So I am sure I can glean some useful info
@Bruce_Chandler (I think) built an arch stone bridge out of foam, and it wasn’t the sun, but squirrels, that finally got it.
I think it looked too much like stone and the squirrels were convinced that they could sharpen their teeth on it! (Even after repeated attempts… 
)
Fortunately squirrels are only a transient problem. We see one a couple times a year and that’s about it.
How many do you want? I’ll box up a few dozen and send your way 
FWIW, 15 years ago I built a culvert for my layout. The ends were 1” blue foam. I covered the exterior with a thin layer of concrete carved to simulate stone. The interior was brushed with Quikrete Crack Seal. Here’s what it looked like prior to installation.
I learned about sealing everything the hard way. On a previous layout I built tunnel portals the same way without sealing the back. When I tore up the layout and removed the portals, I was shocked to find out there was almost no foam left behind the concrete. I would guess that some kind of insect found it amusing to build tunnels or even eat the stuff. Here is what my current culvert looks like after 15 years on the ground.
Great advice. I had considered that I would need to seal EVERYTHING and now I know what to use.
Devon, here’s a hypothetical. If you HAD to… let’s not argue the Why, let’s just say it was a non-negotiable…
How would you make a large layout building do double duty as a squirrel trap?
Live trap or “kill em” trap. It would be interesting to design one of the doors as a guillotine
I’m diggin it. The French Revolution kinda gave guillotines a bad name, which might be why they’re still sometimes underrated as deterrents.
Bonus thought: you could make a small pub or hotel next door called the “Half Squirrel.”
I’ll look forward to your design!
