IKEA is a chain of home furnishing stores. It originated in Sweden but there are now IKEA stores all over the Western world.
So far I've built three 1:48 scale houses from IKEA's 14x19 cm (5.5"x7.5") display boxes: Modern house , Tudor castle, and Bridal shop. My model of my nephew's home is contained in an IKEA box. Also, my H0 scale Moomin house was originally contained in an IKEA display box, and so is the 1:160 scale Year of the Dragon roombox.
I've used plywood, balsa, and cardboard tubes to change the shape of the basic box. This is quite simple as the type of boxes I use is all rectilinear with no fancy trim - just a plain wooden box with a glass front and a removable back. I've used 4 mm (5/32") plywood for most interior floors and walls, but there's nothing special about that thickness other than that it's readily available locally.
After enhancing the shape to incorporate sloping roofs and other features, I've covered it with patterned paper or card (brick and stone patterns from the model railroad shop), sand paper (painted, for stucco), wood siding, plastic sheets of roman tiles, or other suitable materials to give the exterior the look I want.
IKEA's boxes come in two sizes. The small one is 14x19 cm (5.5"x7.5") with a depth of 7.5 cm (3") (exterior measurements). It has a fixed glass front, is back opening, is made from unfinished wood, and costs much less than any craft store shadow boxes I've seen. The large one is 20.5x31 cm (about 8"x12") and has a sliding glass front. I think the smaller size is just right for making a 1:48 scale house of two or three floors, depending on how you turn it. I haven't finished a house using the large box yet; the sliding glass front makes it easier to furnish but trickier to finish the exterior.
These little houses are addictive! But that's not what I wanted to warn you about... miniaturists know everything there is to know about addictive hobbies, right?
I used to have trouble getting paint and wallpaper to stick to the back wall as it's covered with melamine, so I've usually replaced the back with a piece of plywood. But a lady in an online miniature group pointed out that a high adhesive primer should solve the problem. I tried the primer when I built the model of my nephew's home, and it made a big difference!