If you are installing end walls they need to be hung before you pull the plastic over the top. When installing end wall plastic you need to bring your plastic level across the front framing but then wrap your plastic around the inside of the arch so the plastic will hang over your end arches in the same direction as the top cover. Put only a few clips on your end wall cover to hold it up as after you pull the cover over you will clip off both the end wall and the top cover with the same clip. Make sure its level and centered so you have plenty to attach at both sides.