First, I would say it depends on the wall construction, and the deck in the back would give some assistance.

It almost follows a hammer beam configuration but minus some pieces. What is worse than a hammer beam truss? A hammer beam truss missing some pieces.

With the recent thread on drift applied and my dislike for buildings without ties at the proper level, I give it a thumbs down.

Maybe put some sheet metal on it somewhere

Now at 20' you can push some luck or see a qualified engineer.

I see the rafters bending just below mid point from foot to tie. The ends of the arched braces are thin and wood was removed from the rafter for the housing and the mortice, less section there.

Tim