I have found that, with pole buildings, much like with insulation, you can pay to have it done cheaper than you can buy the materials.
I have had 3 pole barns put up on my property, and every time, I am just amazed how fast and cheap they do it.
In one day, they have all the holes drilled, posts braced in place, and the next morning, they pour the concrete. By the end of the first week, the framing is usually all up. Engineering is included. We once had to pay and extra $200 for custom engineering, as my wife wanted a very particular roof construction. But I hire engineers all the time, and $200 an HOUR is cheap.
I have also bought courrugated metal siding and roofing myself, from a big wholesaler, who orders it from the factory. And there is no doubt I pay more than the pole barn guys.
At least, get a bid. You will be surprised.
After they are up, I do all the blocking, interior walls, wiring, and custom work- but paying to get the framing and sheet metal done is so cheap and fast, its a no-brainer to me.