A marble magic wardrobe flatpack can be made at a workbench (Bench with lathe only) in the workshop of a player-owned house. Like when making the normal Marble magic wardrobe, this requires 96 Construction, uses 1 marble block, and gives 500 experience. The flatpack can then be used on a magic wardrobe hotspot in a Costume room, either in building mode or not. This requires no Construction level and gives no experience.
The cost of making and selling a marble magic wardrobe flatpack from scratch gives a profit of: -167,218
After completing the hard Fremennik achievements, they can also be traded to Advisor Ghrim in exchange for 32,500 coins being added to your kingdom's coffers in Miscellania. See Flatpack: Miscellania reselling for details.
See Magic wardrobe for a list of armours that can be stored.