Thank you for your question regarding Thuja plicata x standishii 'Green Giant'!

Green Giant makes an excellent hedge in the height range that you specified, with just a few things to bear in mind. 

Pruning at least annually will be required, as Green Giant can grow up to three feet or more each year under optimal conditions, and just an annual pruning should suffice if you aren't looking to strictly control for appearance. This annual pruning should be performed in late winter after the previous year of growth has had a chance to harden off.

When trimming to maintain the hedge size and appearance, it's best to have a landmark (like a fence, light post, mailbox, roofline, etc) or something to compare against to make sure that the hedge doesn't slowly expand in size unnoticed; since these Arborvitae grow up to 60' tall and 18' wide at maturity this "size creep" is likely to happen over the years.

More information regarding specific pruning practices and Arborvitae in general can be found below:

https://extension.umd.edu/resource/pruning-shrubs-and-hedges-home-garden/

https://news.oregonstate.edu/news/arborvitae-stands-tall-easy-care-hedge

https://plants.ces.ncsu.edu/plants/thuja-green-giant/