Lead lining is a building design technique developed by Magnus Godrikson to protect against scrying.
The exact technique for reliable lead lining is a closely-guarded secret of Wayland Industries. What is known is that buildings constructed using the technique must be made as fortified structures, and the cost of the lead-lining depends on the floor space, wall length, and the number of doors. Windows are not feasible with lead-lined rooms, and rooms created to be lead-lined are effectively airtight, so the door must be opened periodically to allow fresh air in.
Lead lining costs 18 gp for every 5 ft. square of floor and ceiling space, and 18 gp for every 5 ft. long section of 10 ft. tall wall. Lead-lined doors cost 50 gp, including the special work needed for the doorway. Two thirds of the cost is labor, one third is goods.