I know this is a little buried - but I own a truss manufacturing operation and I'd totally recommend finding one to talk to. If you can find drawings, or sometimes even just sketch out a floorplan (we frequently build out barns or other simple structures based on literal napkin drawings) we'll give you a layout of all the trusses, joists and beams that you could take and just stick frame it yourself based off. Naturally we're here to sell trusses, but I think most plants like us are always down to help out folks in the community if we've got the time.
Is the price of a truss fairly linear or is there a length where the price starts to really accelerate? I'm considering building a 30'x60' pole barn with 18" or 24" eaves making the trusses 33' or 34' long.
It's fairly linear for the same kind of truss, like say a 15 foot span to a 20 foot span - just think bigger triangle. Past a certain point, in order to support the shear/wind/snow loads across a span requires increasingly higher grades and width of lumber and you start getting into non-linear territory. Pole barns are an extremely common order for truss plants, and that size should be pretty standard. In single family houses, though, you start getting into "features" pretty quick which affect the price quite a bit, think ceiling trays, HVAC platforms and so on, so you're pretty quickly into some nonlinear territory there as well.
