Troleu,
Are you certain that you can't drop any posts into the building's interior? It would make the engineering an order of magnitude simpler.
That's not to say it can't be done. I've spanned longer. It's just a lot more complicated to cut a trussed frame like that. More complicated engineering, more technical high performance joinery, etc.
If you could deal with center posts. You could potentially support common rafters at the peak, making the building very simple to engineer, cut, and raise. That would be the "sever gordian knot approach" of completely sidestepping the complication issue.
The frame that you are proposing is pretty challenging for someone with minimal experience. Which is not insurmountable, but you should realize that going into it. I would say that king or queen post trusses will be the simplest for this pitch and span, but as others have already mentioned, have them looked at by an engineer.
We'll look forward to more questions!