Talked to these guys.
Few relevant pieces:
The purlins are 2x8s on end, and go over the trusses. So that adds a notable height loss in itself.
The trusses are between 20-24" thick (tall?) depending on snow load needs. Plus whatever loss due to the angle and trigonometry.
In my case with the purlins wouldn't be a problem but that truss would be a head-knocker anywhere except in the very center.
However I asked about purlin length/span between trusses. He thought for my snow load neeeds they can be up to 14'. I have to confirm county requirements and live vs ground, but if I can get away with that then I'll truncate my loft to a 14' span so it is between trusses. Worst case I'd put then at 8 or 10' (also have to work out garage door placement) and just have the 1 that breaks the space.
For the record they usually sell the kits as eeverything but the wood, you buy the purlins locally to save some $$.
They currently have a special for a 30x42 for $15k (before doors, windows purlins etc
