Aligning body panels

I'm trying to get the cab and the fenders aligned properly on my '85 Ram. Anyone have a procedure to follow on where to start?

My garage floor isn't level it tappers toward the middle toward a drain on the floor. So I'm thinking I should have the truck sitting level on its wheels, Or should I get the frame level, or am i over thinking this all together and just start with the doors and work my way forward and just get the body lines straight and the truck being level doesn't matter so much?