Dollieh Sanctuary

Is there a place to find ready made boxes that are at least 14 inches tall and wide? I'm thinking about making a narrow stack of rooms for my dolls.

Or is there a tutorial that can be done with foam core?

great link! Now I'm all inspired again.
I tried to use foam core board like this for my SDs, but I have trouble finding pieces large enough. So I'll be "helping" our local political boosters clean up their signs the day after the next election
I'd want one piece 3ft x 5 feet and one 3ft x 3ft. Good thing I have a large room to do doll stuff in!

Clea Bella makes room sets with magnetic interchangeable walls. They're a little pricey but everything is ready made and easy to change out and they even have magnetic windows and doors to attach so there is that. I think they're scaled more for 1/4 though so some scenes might be too tall.

A friend of mine had a set of foamcore rooms done that were fairly nice, and my gram and I used to make backdrops for meet ups in many different scales. Just about anything that is for 1/12 scale dollhouse boxes could be scaled up easily. Almost all techniques can be used, patterns just need doubling, and its actually sometimes easier to do in larger scale. Also check out the local craft shop's scrapbook aisle for deco stuff. Scrapbook paper is great for wallpaper and flooring, it comes in a lot of textures and designs and is usually pretty dang cheap. The different embellishments are great too, I know Michaels has a ton of vaguely steampunky stuff that would work great as architectural trims and framing plus all the little themed stickers and whatnot that can really add some detail.

Any tips for making a stack of room boxes? I'm wanting a several story tower of rooms.

Shelf sets might be easier than foamcore for a stacked set, simply for weight considerations. Foamcore is so light that it might easily tip over when stacked into something narrow like that, plus the floors might buckle with repeated use. Cheap plain shelves with adjustable height actually work pretty well for an apartment-like tower. Keep the foamcore or cardboard idea to it though, because you can make insertable papered walls and floors with it or interior dividing walls that just slide into place. Take a look at the old American Girl Minis for ideas on how its done. They were simple 1/12 scale roomboxes with many separate kits of interiors that slid in and changed it to be a living room, a bedroom, a barn, a diner, etc.