I made this with one skein of Spud and Chloe fine and had 2g left over. The idea is to weigh your yarn, increase until it is 50% used then start decreasing. I judged it pretty well.
The final size was about 130cm across and 50cm deep after blocking. The advantage of using a yarn with silk in it; growth on washing.
When using this yarn remember it is only a 65g skein. I always assume a skein of sock wool is 100g so I caught out with a smaller skein than I thought I had.