yes, and another idea

While I've used gatorboard a few times, I think placeholders are more easily and suitably made with foamcor.
If you transport your layout or parts, gator board may be just the ticket

My layout doesn't move and the  standins are foamcor.

For tutorials, I send folks to RC aircraft hobbyist site:

Flitetest.com  look for tutorials. The instructions apply to their laser cut foam and any you create with a sharp razor blade.  They even do curves.. like wing profiles.

Gator Foam board

I've been using Gatorfoam since 1992. Have built many of my HO scale steel mill structures using it. I used 3/16'' kraft color and once the basic shell was done I painted them with craft paints. Later on I covered them in scribed styrene and detailed them. They do not warp and stand the test of time. Use hot glue to assemble them and put some stiffners in the corners for long term stability. The largest structures are my rolling mills and they are up to 8' long and 18'' high. Great stuff to work with !! ---  Ken 

Gator board is tougher than plain old foam core

And more water-resistant. I've used both and recommend Gator board for any wall longer or higher than 6 inches actual size.

Foamcore, water + unsupported lengths...

Dear MRHers,

Um, a quick spin with "foamcore benchwork" in the Search box at top right of this page will given a number of threads where Foamcore moisture and "unsupported span" performance has been rather exhaustively tested.
Suffice to say "_full_ immersion (flooded basement)", "literally dripping-wet scenery applications", and "O scale Brass 4kilogram O2R Challenger VS 16" unsupported foamcore span" has been tested and successfully proven for over a couple of decades now...

That said, if GatorBoard is available in your area, and works for you,
then by-all-means, use what you got/are comfy with...

Happy Modelling,
Aim to Improve,
Prof Klyzlr

How many stories tall is that building?

20 inches tall is a lot for N scale.  Gator board could work. Sheet styrene might be better since the walls and other parts could be thinner. and easier to join. Gator board is not a cheap product so styrene might cost less...DaveB

Check out

Checkout http://www.gatorfoam.net

Thanks All

@ Ken. This too is for a mill project, the basic oxygen furnace building. 

@ Dave B.    Error on my part. At the peak it will be only 12" high. 

The only issue I have had with foam-core is it seems to never be "true"  I know it is not designed to be a industrial model material so I am not complaining, but the few sheets I have bought all were warped to some extent. 

Foam core versus gatorfoam

Foam core will warp over time especially in long lengths. Gatorfoam will not !  I have large mill buildings that are almost 30 years old and have had no warpage issues what so ever. They range from 2' to 8' long and close to 12-18'' high. Using just styrene requires a good bit of bracing if you use under .080. I have had a few styrene buildings roofs curl up after a few years.  Yes Gatorfoam is more expensive but well worth it. -------- Ken 

Cellular PVC

Perhaps put this term in the search box and look at discussions. I've discovered this product that was also termed 'foamed PVC' , and i'm rather happy with it.,...used it to construct a turntable pit, and using it on my stone arch viaduct bridge.