First have the tank or pipe level, then the two end pieces should have right angles on them the top should be level and the door side should be plumb. If all these are in place it is exactly correct.
jm2cw
Current Smokers: Backyard RF Offset and Hybrid RF Offset trailer rig with Cowboy cooker and fish fryer, always room for more........
One piece??? Are you talking about the frame for the doors?? My original question was about putting the actual sides of the cooking chamber on and how to get them identical on each side.