Hi Danny,
If you have a really, really flat table, and are very critical in getting everything "right", then blocking up/pinning the wing to build it is fine. I think that most people who have not built a few hundred wings will be better off using a jig and setting it up straight. Building in halves, or a "complete", wing doesn't make a WHOLE lot of difference for most wings, just joining the two halves straight is crucial.
Big Bear