As with Mike from Milford Bay my bathroom also had walls that were out of square by about 1/2 inch. I almost went the way of expensive shimming until upon careful studying of the plans (with no words, all pictures) I realized that the design allows for adjustment for out of square walls. I just finished installing my shower (and I am an amateur) and the adjustment worked fine. Each side of the glass panel is constructed of 2 pieces of extruded aluminum that tuck inside of each other. The top or bottom can tuck in farther than the opposite end, thus taking up the slack. Mike I hope you see this before you start to shim. It may not be necessary. The directions say that it should only take 60 minutes to put this shower together. What a joke! Just working with the shower base and the self-leveling cement took me half a day to do it right.