So long as you can get timber members long enough to not require a splice, that might work. I'd still try and get an engineer to size some scissor trusses though. Hand him $100 to make up for not buying them and I bet your local (non corporate) lumber yard would Calc something up for you to use as reference. You might even find some illustrations of off the shelf designs that match your roof pitch that you could use as reference instead.
It's not impossible to do the calcs yourself if physics was ever a strong suit. I'd still want someone to double check my numbers though.
It's a big deal because you don't find out it wasn't right until snow or rain or leaves brings the barn down.. Or even worse, it gives way while hanging insulation and ceiling panels.
