[Rodger Knox]

There's at least two schools of thought here. The first is the brace is flat and the top is forced into a curve by gluing the braces with a curved caul. Since there is some springback in this method, the radius of the curved caul is less than the desired arch on the top. There is also residual stress induced in the brace/top from two flat pieces forced into a curve and glued, and all of that residual stress acts on the glue line. The advantage is that the braces are "pre-stressed" against the string loading of the top.

The other method has the brace curved to match the desired radius, and a matching curved caul (or radius dish) is used to force the top into a curve for gluing. This method results in less residual stress, and is easier to get consistent geometry for the top dome.