To start creating your sinamay brim you need three layers of sinamay or four if you are creating a large brim. Make sure you cut the sinamay on the straight. If it's a simple you can iron the sinamay layers together, but for more difficult brims block each layer separately. When measuring the brim make sure you take the tape measure in side the brim. Pin the sinamay in North South East and West. Ease the bias round the sides. Leave two cms inside when cutting away the sinamay.
Fold over a small equal amount all around the edge of the brim (about 1/2cm) using the back of a spoon and put brim wire inside. Using a sewing machine zigzag(2mms) stitch all the way around the brim.
For me I think it would be expensive to purchase brim blocks, as I don't know whether I would ever use them. I would probably buy them ready blocked and explain to the customer that they are hand blocked but just not by me. Also I seem to have an allergy towards sinamay, it's not my favourite material.