Although the birds hop up onto the roost bars, they fly down, so they'll need at least as much horizontal room to fly down, as the height of the bars. I've mainly had smaller breeds than yours, and I think 4 ft is way too tall--I'd go with 3 ft or even 30 inches and 24 inches. Some people who keep your big breeds would know better though as to how low to install the roosts, to prevent injuries flying down. I'd think 18 inches away from the wall is plenty though, and having different heights could prevent squabbles.