Basic truss design for outbuilding
For small buildings like this I'm not a load calculations guy. I'm a seat-of-the-pants experience guy. This is because lumber is usually grossly oversized for such short spans anyway, so it comes down to your carpentry techniques.
Yes, that design is plenty stout from a lumber standpoint (even 2x4 rafters are plenty), but you must fasten the joints together very well. Due to the steep nature of your roof and the lack of direct rafter bearing (without a bird's mouth cut) there's a lot of shear force on that connection. Nearly all the roof load gets carried by the fastening.
I might use three 2-1/2&quot; construction screws from each side of each joint. For a lesser sloped roof with 2x4 rafters I've even used timber screws through from the top into the wall plate (with countersunk heads). Ecnerwal rightly points out that construction adhesive is a good idea here. I've used it for OSB gussets. It'll add a lot of rigidity to the connection.
Whatever you decide, it needs to be stout. If you bounce your weight on the peak and there's any flex at all in the joints it's not good enough. Do that right and you'll be golden.
One other tip: Build all trusses from the same prototype (jig) and mark the ends so they stay oriented. Trusses are rarely perfect and if you swap ends with any you'll have a wavy roof and fascia.