Measure the size condensate pan you need and add 2 inches to that measurement. For example, if you need a 30 by 30 inch condensate pan, increase the size to 32 by 32 inch. This will be your cut size for your sheet metal.
Cut a piece of sheet metal at the above increased measurement. Make sure all the corners are square.
Notch a 1-inch square out from each corner. To do this, measure in from each corner from both directions 1 inch. By doing this, you will create a 1-inch square at each corner. Cut this out with your snips. Notching out the corner will allow you to bend each side up to make the condensate pan.
Slide your piece of sheet metal into your brake until 1 inch is left sticking out. Clamp it down and pull up on the arm to bend the protruding material up 90 degrees. Repeat this process for the following three sides and you will be left with a pan with 1 inch tall sides.
Solder or weld the corners on the pan to make it water-tight. Soldering is preferred for light-gauge pans while welding works great on heavier-gauge pans.
Drill a 1/2 inch hole in the bottom of you condensate pan where you want the drain pipe to connect to. Bolt a 1/2 inch pipe flange and gasket to the bottom of the drain pan to allow for a drain connection.