I have a one car detached garage with a gable roof. The gable ends are on the sides and the slope of the roof is on the front and back. I have to repair a lot of insect damage. So far I have put some temporary supports in the front and removed the entire front wall. The door opening is 9' wide. There is a double 2x8 header with two 2x4 top plates. Here are some of my questions. The door is not quite 7' tall. Could I eliminate the 2x4 top plates that are on top of the header and have the header only support the roof rafters? This would give me some extra height and I would be able to get a standard 9x7 door. The foundation is block. I am planning on adding an extra course of blocks on the front so that I can get the sills up off of the ground. Yard slopes off towards the back so the height issue is mainly on the front. I need to build the side jam studs to go all the way to the garage floor to attach the overhead door tracks. Should I build the rough opening for a double jack stud on each side of the door and then have the king stud on top of the block or will one jack stud leave enough room for the track? Hope this makes sense. With two jack studs I would leave 9' 7 1/2 inches between the blocks for the rough opening. 9' for the door, 3" on each side for the studs, and 1.5 inches for the two 3/4 inch trim boards. Or would I use 9' 4 1/2 inches? 9' for the door, 1 1/2 inches on each side for one jack stud, and 1 1/2 inches for the two 3/4 trim boards?
Common practice is to mount the tracks to a 2x6 mounted flat on the surface of the wall. If you were to mount the track to the studs, I might consider a 4x4 or similar post rather than two 2x4's. This would minimize the possibility of splitting the stud when the lag screws are inserted.
A 4x4 has a higher liklelyhood of bowing and twisting.
I would use a double jack and pre-drill for the lags.