Don, I went to Mt.Airy and talked to all three, they come out of one factory. I bought factory direct with cash, not check but cash. I had them to build me a "Certified" carport. This means that the plans fall under NC building codes with a 25 year warranty. This cost $400.oo extra. Mine is 45ft long and 15ft.inside clearance. 12 ft wide is the same price as 18ft wide! Mine is 18ft. wide. Two guys came out and built the thing in one day for $300.oo labor! You are stupid not to let them erect it. mine came to a total of $3,200.
If they don't have to cut the roof panels you save money.
If they don't have to cut the rafters you save money
if they don't have to cut the uprights you save money