I built mine with 1/2" and wouldn't go any lower. 1/2" is much sturdier. I used my bottling bucket to mold it around and now I have a 50' 1/2" chiller that chills my wort to pitching temps in about 7 minutes. Of course my groundwater temps are in the low 50's, so that helps.
On Tap: Hobgoblin, Coffee Stout
Bottled: Arrogant Bastard clone, Summit IPA, Apfelwein