Basic wall units are called flats (just like in the theatre) only the frames are built on edge and covered with a thin plywood (sometimes called door skin). You put enough flats together and you have a wall. The camera obviously can see closer to these walls so they not only have to be covered with something (texture, wallpaper, surface decoration, etc.)you have to be careful about the spaces between the flats since they are usually made in 4' wide modules because that's the normal width of the plywood. One of the ways you can always tell a set wall from a real interior wall is by all the jogs or angles in the walls. Sometimes they are small jogs only about 1 inch and sometimes maybe a large architectural element like a pilaster (engaged column) to break the flatness and hide the seams. These jogs are so you don't have to cover a flat seam and sometimes to be able to take the wall completely out. These are called "wild walls" and are designed to be removed from the set so that the camera can shoot from a different angle and not be hampered by the wall. It's the only way you can film inside a small room or space. Even when Tom was crawling in a tunnel, one side of that tunnel was open for the camera and could be put back later.
Many of the Magnum permanent set walls had a form of plaster (usually dry wall paste) we called mud. I did address this in an earlier post, but it created the look of rough, aged plaster and also bridged any gaps in the walls made up of smaller flats. Many walls were wall papered and sometimes painted walls only had something like masking tape that was painted to cover the crack between the flats. This seam could always be cut with a knife if the wall needed to be taken out. They sometimes pre-painted more masking tape if they had to recover it if the wall went back in place.
The basic construction framing material is wood--weather it ultimately looks like marble, stone, brick, or tile. Tile was usually ready made wallboard tile or sometimes even scored masonite which is sort of a thin fiberboard with a smooth surface. So 500 words later, it's time to answer David's question about bricks (are you still with us David?). By the time Magnum was around, Universal Studios had one of the best molding (moulding) mills in Hollywood. They could make just about any kind of trim. They also had vacu-form wall surfaces like bricks, stone, and things like "dirt skins" for caves and exterior ground. As I recall, the bricks in Higgin's den were vacu-form plastic (heated plastic sheets over a form, air pulled out, plastic conforms to the underlying shape). They came in large sheets and could be painted. They also had "Z-brick" which were a fake brick veneer, but only came in about 3 or 4 variations. Got any old pancake houses near you? I do and it's still full of Z-brick. (sounds sort of like "brick" with a French accent). It's getting late...... Another way of doing bricks (we used this in the theatre a lot) is to take a large sheet of 2 or 3" thick styrofoam (sometimes used for roofing insulation) and a rough file or rasp and digging out the foam for the grout area. You can do large blocks of stone or smaller bricks or even stones with this. Sometimes a soldering gun with a wide tip is used--but it does give off a toxic gas when it melts the foam.
The 1970's and 80's had a lot of things like "Mediterranean" spindles, geometric plywood cut-outs, filigree panels, and other peculiar architectural elements that were used. Often times you would see some sort of "entrance screen" into a room near the doorway. These were used to help block the view beyond the door when it opened or to see the bad guy hiding before the good guy did or sometimes for the camera to shoot through. Furniture and architectural elements located near the camera in the foreground are called a "cutting piece". It's a way of providing foreground interest or sometimes to create the illusion of the 4th wall when all there really is is a low cabinet with a vase on it.
Thanks for staying with me if you did. You can pick up your diploma on the way out.