As an inspector, I would look really hard a site-built truss if I encountered one. Its design and construction would have to be substantiated by an engineered design, stamped by an engineer.
It can be done, but you'd better have your ducks in a row. If you're in an area that requires permits and inspections, chances are the building official will frown upon it. Then you're looking at hiring an engineer...Who will hopefully sign off on your design after charging you hundreds of dollars to consult in the first place.