I need to replace a 6"x12"x12 feet BC Fir carport beam.What could I use to laminate a substitute beam?

Is it a full 6" or 5 1/2". I'd use 3 2X12 with 1/2" plywood between the 2X12. That will =5 1/2". If it will be outside, use pressure treated lumber and plywood. Carpenter bees won't eat it. What is wrong with the old beam?