Woulld be great if your printing instructions included 1/24 and 1/20.3 as garden railroad kits for buildings are way over priced and too Lionel-like for my taste..

Charlie
One of the things you will run into is that the printout is larger than the typical 8.5" x 11" page. To get around that, make sure that your .pdf reader is new, at least 2014. You will be able select to print on multiple sheets with match lines. Also, on something bigger than O, just assume that you will have to re-enforce the walls, etc. Also, I'm assuming that you have an indoor layout. Remember, without some precautions, paper is NOT outdoor friendly. You can try a product made by Rustoleum, called NEVER-WET. It is a two part spray product that will put a water-proof coating on your kits. You have to learn how to use it, but it works pretty well.

Oh yea Charlie. It's been posted on this website many times. Take the size you have and divide it by the size you want and the percentage you get is the percent to print at. E.G. 48 / 20.3 = 2.36. Therefore print at 236%.
Good luck.

I've used a papercraft model as a template for building a garden structure out of insulation foam. In this case, I used a Fiddler's Green kit, but the technique is the same no matter what papercraft model you start with.

http://miniaturearchitect.blogspot.com/2014/02/blog-post.html

http://miniaturearchitect.blogspot.com/2014/02/still-working-on-garden-railway-building.html

http://miniaturearchitect.blogspot.com/2014/03/garden-railway-shop-pt-3.html

http://miniaturearchitect.blogspot.com/2014/03/a-few-outdoor-photos-of-completed-model.html

Oops, one more link, with some detail pictures.

http://miniaturearchitect.blogspot.com/2014/03/a-sunny-day-so-i-took-last-of-photos-of.html