Step 4: Build a strong foundation
As mentioned, I paid someone else to do the foundation. It cost in the neighborhood of $6k. Worth every penny.
Be sure and talk the plan (pictured below) over with whoever is setting up the site so that the garage gets poured in the right spot. They know their business, so ask for their advice. In my case, there was a utility pole that was interfering with the planned driveway somewhat. My plan originally called for a 2' set back from the property line, but based on the recommendation of the concrete guys, we pushed it out to 3' in order to clear the utility pole with some cushion. They moved their lines and no sweat, but once the forms are in place moving the placement gets more difficult, and once the concrete is in, then forget it.
The key steps to getting the foundation in are to lay out the lines for the foundation relative to the property lines, and to set up the site for the pour. To get the site ready the hole needs to be dug, the soil compacted, backfilled with suitable class-5 gravel, the forms erected in accordance with the lines, and reinforcement placed in the hole. The photo below shows my site just before concrete pour. You can see the grid of reinforcing metal rebar, the class-5 gravel and the forms.
Before you can pour in the concrete, you will need to have the site inspected by the city. They need to check and make sure you aren't doing anything stupid, are following code, and have placed the structure correctly based on the drawings signed off on by the city during the permit process and in agreement with property survey markers. This inspection will be arranged by the concrete subcontractor and everything should go smoothly if you have communicated with them well. If you are on your own, you just need to put in the call to the inspector and arrange a time. When you get your permit with the city they will give you a checklist for the inspector to sign as well as a phone number for your assigned inspector. Inspectors are friendly and helpful in general so don't hesitate to call and ask them questions. If they can answer a question on the phone it saves them a trip out to your job site.
With the forms inspected, the concrete can go in. One key thing to talk with the concrete guys about is the anchor bolts that will go into the foundation. The building code require anchors to be embedded in the concrete so that the bottom sill plate of the framing can be bolted to the foundation. There are specific rules about the placement of these bolts. Every six feet, within 12" of any cut in the sill plate, etc. Your concrete guys should know the rules. Make sure they know and clearly make where you are putting in your access door(s) and overhead door(s) so they can place the anchors correctly. In my case I had to have a single course of block around the foundation so that also required communication so that the openings would fit my doors.
After a day or so the concrete guys will come and take down to forms and clean up any spilled concrete. Be sure to communicate any concerns you have about the job if any at this time because this is the time that they will be expecting to get paid. Sometimes you will pay half up front and half upon completion. Once they get the second half of the money it can be hard to get them to come around and correct any problems so speak up before you write that check.
The next inspection you will need is the framing, so after a few days (~4) to let the concrete cure you can start building. Right about that time, you should expect a bunch of rain. Actually the rain will probably start as soon as the truck driver who delivered your lumber drives away.