Q.What plants do you suggest I put behind this structure (shaded) that will reach a good height and give security and privacy?
There is a small gap (about 600cm wide) between the back fence and the back wall of the outhouse. I am looking to increase the perceived ‘height’ of the back fence so that we get some increased privacy, security and that also looks like (that big roof looks horrible right now). Was thinking papyrus grass but that only blooms summer to autumn right?

Certified GKH Gardening Expert
As long as there are no restrictions in your country on bamboo... I would HIGHLY recommend this as a fast growing, versatile, and very hardy privacy screen. There are varieties in all sizes and colors, so that you can choose one that suits the exact needs of that spot.
This article will help with the care of bamboo: https://www.gardeningknowhow.com/ornamental/foliage/bamboo/caring-for-bamboo-plants-in-your-garden.htm