Through-wall roof scuppers are used in two circumstances. The first is for roof drainage where a gutter is ruled out for whatever reasons. The second is a backup system in case roof drains clog to prevent roof water from accumulating excessively and collapsing the roof structure. 
In each case the scupper extends through a parapet to allow roof water to drain either into a conductor head and downspout or simply down the face of the building in the case of overflow scuppers.
Some codes require a secondary roof drain system as backup to the main roof drains. Scuppers may eliminate the need for secondary overflow roof drains. In extremely large roofs, scuppers may not be feasible.
The traditional material for scuppers was copper for its durability. Today it is stainless steel for an equivalent quality without the risk of robbery.

Roof Access is critical in commercial buildings especially if there is mechanical equipment located on the roof (flat roof). The traditional 30"x36" roof hatch and vertical ladder are inadequate. Maintenance of both the roof and the equipment located there require easy and safe access for inspection and bringing tools and filters onto the roof. The taller the building the more necessary this roof access becomes.

A Ship's Ladder and Roof Hatch are the least expensive way to meet this need for maintenance access.

Very High Ladders require require special consideration of OSHA regulations. A cage around the ladder may be required if the rise is more than 20'.