I have been involved in a lot of fashion shows over the years. Mostly due to I started creating stage and theatre designs to make ends meet while taking my first Fine Arts Degree. Most catwalks are not permanent installations - personally I have never see one. They are usually made from cross braced metal angle iron, tubing or 2x4 wood framing - custom made or purchased that is bolted or nailed together with a floor (plywood painted or covered with linoleum, carpet or what have you). This makes the staging versatile for a fashion shows; convention stages, rock bands and it then can be moved to any location such as hotel ballroom, convention center, sports arena or whatever. The Stage or catwalk has a stage right and left and is then dressed up with backdrops, skirts around the bottoms, lights, flowers, etc. to make it look pretty.