My mother came over yesterday and helped me lay out and pin the tulle for the second set of tutus for the niecelet. For anyone thinking they want to adapt the Oliver and S tutu to 54" wide tulle, here's what I finally ended up doing.
I used three yards each of up to four colors. Three yards gives you a full 108" to work with. Start with your first color, unfold and lay out flat then refold into thirds along the shorter edge. This gives you three layers that are 108" wide by about 18" long, depending on the accuracy of your folding.** Repeat, stacking the next three colors on top. Make sure you have as even an edge at the top as you can get, because that's where you'll sew the gathers and the waistband.
A very long table and/or a second set of hands is necessary here. Also, we pinned as we went, rather than waiting until it was all stacked up. This was very helpful. When you get to the subsequent colors take the first raw edge and pin it all along the top first, so you have a stable fixed edge to fold the thirds from.
Once it is all stacked up use the rotary cutter and mat to trim bottoms so you have a cut edge on all layers and to even up the sides if needed. You don't need to trip the top because you will cut it after you've sewn the gathers and the first ribbon.
I made every mistake possible on the purple one, including cutting the waistband ribbon when I was trimming the top. For the love of God. The instructions only advise to be careful here at least twice. I mended it with zig-zag and tried to get over myself.
These are both made with four colors which results in twelve layers of tulle. Yes, twelve. The pink is: dark pink, medium pink, and two layers of light pink. The purple is: dark purple, two layers of light purple, and light pink. It looks like a sugar plum, totally charming.
If I did this again I would go with only three colors, which would result in nine layers of tulle. (The version in the O and S book calls for ten layers.) I think twelve is a little, well, full. It's lovely and all, but sort of over the top. In the Oliver and S discussion forum it is clarified that the tutu can be made using 54" tulle as the width, and I did try that, and it ended up very, very cute and all but without the drape or fullness that I really wanted. Okay -- next up, I think, one of the art smocks, maybe the one with bias tape. I'm trying to gear up for Kids Clothes Week at the end of April.
** The "width" here is the dimension that you will gather and turn into the waistband. It is the long edge. The "length" is the dimension that will eventually be, well, the length of the finished tutu. It is the short edge.