The garage door has to be 12x12ft and I need at least 12in of space between the top of my door opening and the ceiling. What changes do I need to make to the traditional framing techniques to support this wall height? Do I need to jump up to 2x6 studs or will multiple rows of horizontal blocking suffice?
The most important question here is, 'do you have a building plan?" Building a structure with 13 to 14 foot walls and a 12 foot door is quite a reach for an inexperienced DIYer. You should start by selecting a set of building plans at your local lumber yard or maybe online. There are a lot more considerations than what size studs you should be using. You are going to need a foundation detail to support the added weight of this large building. The wall details will most likely be 2X6, fire breaks, and 1/2" to 5/8" sheathing, ground built then lifted into place. Your design may use roof trusses or rafters with collar ties, and substantial posts and headers for a 12 foot door.
A building of this size is most definitely going to require a building permit. To get this permit, they will need to see your blueprints or plans.
With all that said, I personally would not build 14 foot walls with 2X4's. I would use 2X6's 16"OC, horizontal stiffeners 48" OC, 5/8 CDX sheithing, double 2X6 plates(upper & lower) and an engineered truss roof. Door headers minimum of 4X12 @ 12 feet, preferably a LAM.