I just completed the first Parti Gyle brew , I did a Bi re De Gardie and then a Belgian Pale Ale then finally I capped the grains to make a Toffee oatmeal stout. I really like this method of brewing because it makes sense that your brew day will be longer but your saving time by only making one trip to the beer store and clean up is about the same using this method. Also it is cost effective.
One web page I found has a spreadsheet that you can use to figure out a batch size and the page also has other links to Parti Gyle websites. I will tell you that this is the only way that I think that I will brew from now on. this is the site : http://www.sonic.net/~ctweney/parti_gyle.htm
Definition: Parti-gyle is an archaic brewing technique wherein sparging does not occur. Instead, after the wort is drained away in parti-gyle brewing the grains are re-mashed for a lighter beer. Depending on the quantity and quality of the grain, this can be repeated three and sometimes even four times. The first beer is strong and robust, while the second is milder.