At last, we're getting to the fun part!
There are different ways to assemble the walls. Some people choose to build the walls as they stand, others like to build them on the ground then lift them into place. I chose to frame the 2x6's on the ground, except for the doubled top-plate. This allowed for the strongest nailing. If I had built the walls standing up, I would have to drive the nails in diagonally from the studs to the sill plate and top plates, not nearly as strong.
Decisions to consider:
It's important to know, before you start, exactly how long each wall needs to be. It's not as simple as it sounds. Each section of wall framing needs to be the length of the foundation MINUS the width of the framing for the next wall. So, for 2x6 construction, each of my three full walls needed to be 5-1/2" shorter than the length of the foundation (we'll get to the wall with the garage doors later).
Identify the First Wall. This should be the wall that is to the left of the garage doors when you're standing in front of the garage looking at the doors. Begin construction with the first (left) wall, then go around building all three full walls in order. After that's finished, we'll tackle the special needs of the front wall.