Glulam is suitable, and should be treated for exterior use (see Glulam Durability)
Treatment options are H3.1 (LOSP) which needs to be painted and maintained, or H3.2 (painting is optional but recommended). The designer needs to ensure that H3 treated timber is not in contact with the ground.
For further information, a local Stratalam supplier (see www.stratalam.co.nz) will be able to help.
Paint suppliers can help with recommended paint systems.