I have wanted to do this!

If I may tag along to ask a question:
If I see a beautiful fabric suitable for OBW, how many yards should I buy - for lap quilt, twin and queen size?

Thanks:)

Right...after arranging the 4little triangles, and putting them in Place on your design wall, sew each triangle to the corner the octagon ....completing a square....tedious, but then sew the rows together is easy....I have made a dozen or so obw...both hexagon and octogenarian....it's my most favorite of all because of the surprises

It depends on the repeat length. For hexagons, you need 6 repeats minimum, and for octagons you need 8. If it's a short repeat length, you need to buy multiple sets of repeats because you won't end up with enough blocks.

The book does lay out how much you need for each quilt size. Six repeats of an 8"-repeat fabric (1 1/3 yards) will make you enough blocks to make a lap sized quilt if you add a few borders. The book suggests, for more variety, to find a fabric with a longer repeat so that you have more blocks and many different blocks.