I have made several of those but I adjusted the way I did the casing because I wasn't happy with the way my first one turned out. Basically I hemmed the top, sides and bottom of the apron and then hemmed the casing pieces at the top and bottom to match the length of the arm hole and then I sewed the casing to the apron by folding the casing in half longways and then sewing to the armhole. I have a serger but if you don't just finish the edge with a zigzag stitch after you sew it on. For me this made the casing look much nicer but then again I am a bit casing challenged LOL.
I also had to bring the bottom of the armhole down about 4 inches because it was putting the ties right under my breasts and that just didn't work for me. If you aren't as well endowed you might not have an issue but its worth checking the paper pattern against yourself before cutting to make sure.
The tutorial is great though and I will never make an apron without a casing again LOL. I even made up my own tutorial using a hand towel to make an apron for kids. Here is the link if anyone is interested
http://www.4shared.com/file/74607021...ildapron1.html
Steph