The Masonry zone is a place for Townsfolk to craft stone items.
When a Mason's Bench is created and placed inside the zone, Townsfolk can craft advanced stone items and utilities such as the Baker's Oven, stone walls and stone roads.
A Masonry zone requires at least a 3x3 tiled zone. Mason's Benches can be placed inside the zone to unlock further crafting recipes. Having the Masonry zone above-ground and surrounded by walls will increase the efficiency of the Townsfolk working within.
An example of a walled-in above-ground Masonry zone, complete with Mason's Benches.