How do i be paid a rough channel for an 8' x 7' garage door? ...

I involve this answered like greased lightning PLEASE!?
Answers:    Your opening should be exactly 8x 7 when finished.
Plan for any mouldings or other finishing wood.

Place a massive header over the opening, or it will settle.
Sprinkler System: One of my zone is...
What that process is the door way requests to be about 1" top to 2" sides smaller than the door you are putting contained by so it has something to trademark against. The instructions should tell you what the rough introductory measurements should be.