What gauge sheetmetal for a patch?

[66FBCharger]

I need to make a patch panel for the rocker panel on my 89 LeBaron GTC ragtop. This is the first time I have attempted to do sheetmetal. I am going to make a bunch of practice coupons so I can get the feel for welding the correct thickness sheetmetal. After I get comfortable doing the practice coupons, I am going to make a patch for the rocker.
What gauge sheetmetal do I buy to match typical original sheetmetal gauge?

[JB400]

Either use a sheetmetal guage or a pair of calibers to measure a good section of sheet metal to find out.  But, by rough guess,  I'd say 20 guage

[tan top]

 mesure it like  S400w mentioned , 
what ever the gauge the metal your going to plate/patch  , use the same thickness

[JB400]

Another thing to remember.  When your welding on a car with a computer, unhook the battery.  If you don't, you'll need a new computer

[66FBCharger]

Another thing to remember.  When your welding on a car with a computer, unhook the battery.  If you don't, you'll need a new computer

Great tip. Thanks!