Hello,
It seems that the Lagassa site is down (the under construction page kept coming up), after about a 24 hour search I found a side site that seems to carry some of the original content from the site (never having seen the original site I can't really know for sure, sorry) It has a good explanation on how to make a standard/smooth gown.
The link is: http://mirrors.itsalwayssomethingwithher.com/stepbystep_ballroomdress/
I've also found some interesting threads on sewing.patternreview.com and danceforums.com with some content on patterns, fabric, and stones.
Hope this helps.

Also if anyone has found other useful sites for constructing ballroom costumes I would greatly appreciate it, if you could post them. Although I'm a proficient sew-ist (not a word), having only minimal access to the pretty expensive gowns which makes analyzing garment construction uber difficult, everyone is so secretive Arg.

The Rhine Stone Guy out of FL has a guidebook as well as how to convert street dress patterns into ballgowns.

http://www.rhinestoneguy.com/

I seem to remember my partner using a brides made paper pattern for the top half and buying the lower part ready made from a firm in London and joining them together.