OK here's a couple of caveats which I've just come across. The yardage given is for a size 38, which happens to be the one I'm making, so no bigee. Secondly, looking at the layouts, the straight grain line is not treated in a normal way. Usually, straight grain refers to the warp threads. The layout has one skirt piece warp-wise, one weft-wise. This affects the yardage if you're using a fabric which won't like you being free with direction - obviously those with nap, but also any fabric where the stronger thread is in the warp. Lots of my duppions for instance have a strong warp but weak weft.
For the future I would def. suggest not getting your fabric until you've checked your pattern from this firm. For me, the plaid I first thought of is out, it was on the short side to start with. I have another plaid I might try, still pondering this. I'm fabric fasting and trying very hard not to buy new stuff until the mountain of fabric lengths in my sewing room has had the summit hacked off it.