An oak bench flatpack can be made at a workbench (Oak workbench or better) in the Workshop of a Player-owned house. This requires 22 Construction, uses 4 oak planks, and gives 240 experience. The flatpack can then be used on a seating space hotspot in the Dining room, while in building mode. This requires no Construction level and gives no experience.
The cost of making and selling an oak bench flatpack from scratch gives a profit of: -1,868
After completing the hard Fremennik Tasks, they can also be traded to Advisor Ghrim in exchange for 112 coins being added to your kingdom's coffers in Miscellania. See Flatpack: Miscellania reselling for details.