http://quiltinaday.com/theater/2300/2301.html
This is how I did mine, but I used a desk and cut the hole just big enough for my machine, so i didn't need a plastic insert like she uses. On the rare occasions I need to use the free arm, I just lift it out and set it on the desk to do the free arm work, the drop it back in the hole. When you make your support shelf, make sure you allow space for your knee lift, if you have one. My husband helped me do this for my Brother straight stitch machine, but I just got a Juki F600 for Christmas, so am sewing on my folding table until he has time to make the hole an inch bigger. the nice part is both machines will fit the table, just with a small gap behind the brother if I want to use it for the bigger harp. Oh, when I'm doing a big quilt, I set my folding table up behind my desk to give the quilt more support, then fold it up and put it away to have more room when I'm just piecing. Works great and I only spent $38. I also did my design wall the way she does in the video, but was cheap and used flannel sheets instead of headliner, love my design wall.