martin20 - I would say that height isn't that important. It mostly matters if people can climb a wall. If you aren't sure about the height, I would recommend using https://www.heightcomparison.com to compare different heights and see the difference in a 3D sketch. When I started to build the wall for my house, I used this app to compare different heights because I didn't want to start before I was sure about what I needed. I made some small mistakes when measuring heights but found out about them before starting building.