Walk In Closets can be regarded a big wardrobe or a dressing room directly.
There're open style and close style, (with doors or no doors)
In general, Walk in Closets have many shelve and drawers, the shape can be L or U, it usually is fill the whole room. Some people also like set a isand into it.
Materials can be HDF, partical board, polywood and solid wood. Surface treatment can be pvc membrane, acrylic, lacquered and uv. Generally, lacquered is used more widely
Compared with Wardrobes, Walk in Closets are more suitable to big apartment or villa and more luxury.