Background:

14’x24′ room addition on the back of a single story house
14′ dimension is perpendicular to house; 24′ dimension is parallel to house
Ran ceiling joists in the 14′ dimension
Ceiling joists land directly over top of ground floor wall framing (2×4; 16″ o.c.)

Wanting to use space in attic as bedroom
Advantech subfloor was screwed on top of ceiling joist and will act as floor of attic bedroom/space

In order to increase headroom in attic for bedroom, I am planning on framing a shed dormer that comes down from both sides of the the ridge.

Common rafter pitch = 10/12
I am planning on coming in 2′ from the gable ends (14′ dimension), as per shed dormer design articles I have read. Combined with the 12” gable overhang, that should place the dormer 3′ in from the finished ends of the roof.

I have done some research into framing shed dormers. I want to run my plan by more experienced framers/individuals. 

I will double up the rafters that will carry the side walls of the shed dormer. I will frame these “cheek” walls and have them rest on top of such doubled up rafters.

The wall of the shed dormer will be majorly occupied by windows. I will frame this wall and have it rest directly over top of the ground floor exterior wall. I doubled up the 2×10 ceiling joists that fall directly over top of the exterior walls (14′ dimension) in anticipation for the dormer wall above to fall directly over top of them. 

Rafters will come down from the ridge and rest on top of the shed dormer walls. The pitch of the shed dormer rafters will be 3/12. The approximate ridge height of the common 10/12 rafters that span 12′ is 10′. With the 3/12 pitch shed dormer rafters, I will be coming down from 10′ to ~7′. 

I understand that I have to prevent the walls of the shed dormers from spreading outwards through ceiling joist/rafter ties but what I am struggling with is how I would accomplish this since the span is 24′. I understand that for trusses, the bottom cord (acting as a rafter tie/ceiling joist) is sometimes joined using pressed metal brackets.

I would deeply appreciate your feedback on my plan and my rafter tie concern!
Thank you, and I hope everyone is having a wonderful day!