Rafter ties or ceiling joists acting as rafter ties are required by code unless the house is designed so that the walls or a structural ridge beam carries the full load of the roof.
Rafter ties for lean to roof.
Simpson strong tie 6 in 18 gauge triple zinc steel rafter tie.
Simpson strong tie 5 2 7 in 18 gauge triple zinc steel rafter tie.
If you are framing a cathedral ceiling there are a couple ways to deal with the need for rafter ties.
You can possibly remove them altogether of you include posts in the gable walls to support a structural ridge.
If your garage is 24 feet wide and has a 4 12 roof the new rafter ties can be placed no more than 16 inches up from the plate without additional engineering.
You can use common rafters on any shed roof but they make the most sense when constructing a gable roof or lean to type shed roof where they can sit on or attach to top plates of a wall.
For pricing and availability.
Simpson strong tie category roof truss and rafter connectors ties and straps for cold formed steel construction.
From a practical perspective it s difficult to use high rafter ties on a low pitched roof because the force in each tie increases with the inverse of the pitch.