All complaining aside, once you get the hang of it and take care in maintaining a straight line of shingles it is not all that bad. There is another good reason to avoid shingling in the heat besides comfort. In the hot sun the shingles get soft and can tear when you carry them or walk on them. Also the adhesive on the bottom will begin to bind the shingles together before you have them in place which can be a pain. So shoot for a cloudy day in the mid 70’s if you can.
Shingling is by far the hardest part of roofing and can be hellish in the heat and sun of summer. Add to that the itchy fiberglass and general abrasive nature of the shingles and you can be suffering like a simonist or sorcerer in the 8th circle of Dante’s Inferno. Again, my mistake in choosing 5/12 pitch came back to bite me as shingles refused to stay put on the sloped roof. Bah!
I used regular 3-tab shingles for my garage since the matched the house. The process is similar for architectural style shingles. The first step is to stick down your starter strip over the roofing felt and ice barrier. The starter strip is like a shingle in roll form without tabs and keeps water from the tab cutouts from reaching the roof deck. Roll the starter strip out while peeling the backing and nail it down every foot so near to top edge. You want the starter strip (and the first shingle course) to extend about 5/8″ beyond your drip edge on the lower horizontal edge so that water doesn’t wick between the shingle and drip edge. The overhang is also important to allow water to drip into gutters if you install them. See the sketch for more info.

There are several methods for shingling. The easiest is to snap a line up the sloped roof in the middle, equal distance from the gable ends. When beginning to shingle, you will start at this centerline and move out towards the edges, staggering the shingles like the OSB panels so that the cuts in the tabs are offset a half tab from the course below. This allows two people to work out from the center towards each gable. You can also start by cutting a shingle in half leaving 1.5 tabs and start in the lower corner. This method can result in fewer measured cuts since if you keep everything square you can cut a bunch of shingles in half in advance and only have to measure the far side. This assumes your roof is square to begin with, so the center method can result in a more even look for the beginner. If you start from a corner, one person can move horizontally while the other builds up and diagonally as the first person’s progress allows.

Each shingle may have a different recommended “exposure” or amount of the single below that shows when overlaid correctly by the upper shingle. Whatever the exposure, you can use that number to snap chalk lines across the roof after you have the first course of shingles nailed down. Measure up from the top of the first course this exposure distance and snap a line. Measure from this line another exposure distance and repeat snapping lines until you reach the peak. If your lines are not parallel to the peak then you have a problem with the squareness of your roof, the lay of your first course, or your line snapping. In any case, you want the shingles to be parallel to the peak at the top so you can cheat the shingles as you go without it being too obvious. If no exposure distance is available from the manufacturer, you can put a nail in the top of the tab cutout of the lower shingle and let the top shingle rest on the nail to get a consistent exposure. This can lead to wandering rows as the shingles aren’t exactly machined to aerospace precision.

You should put 4 nails in each whole shingle. Nails should go right above the cutouts that define the tabs, far enough up so that they are not exposed and just below the adhesive tar strip. See the sketch for details. You want to put the nails in deep enough so that they don’t stick up and tear the overlaying shingle but not too deep that they tear through the underlaying shingle. The nails should go in straight so that the heads don’t cut into the shingles. If you mess up, use the cat’s paw to pop the nail without damaging the shingle and try again. If the shingle gets damaged, remove it and use a new one.

Start shingling as shown in the sketch and work your way out from the corner or from the center. When butting shingles together on the same course, try to space them so that the resultant cutout resembles those on the middle tabs. A little space (1/16-1/8″) will also prevent buckling when the shingles expand in hot weather. When you get to the gable edge, measure and trim a shingle with your utility knife, using your speed square as a guide. Cut from the backside and use a scrap shingle as a cutting pad. You don’t need to murder the shingle, you can cut 75% of the way through and the shingle will easily tear on the line. On the gable ends, try to evenly overlap the drip edge by 1/4′ or so. If your cut shingle ends up with a tiny tab strip you can put another nail in or use roofing cement as needed to hold this piece in place. Be sure that no nails are exposed to the elements as this will provide a route for water to get to the roof deck.

As shown in the sketches you can proceed with whole shingles working towards the edges and upwards diagonally until the bottom courses meet the gable ends. At this point you need to start measuring and cutting shingles. Precision is not all that important, so do your best and don’t sweat it. Continue up the roof, while hopefully another crew works on the other side so you meet at the peak in short order. You may need to trim the top of the last course of shingles so that you cover all the nails on the underlaying course but do not plug up the ridge vent slot. Use the vent as a guide to make sure that you will be covering all the nails with the vent.

When it comes to installing the ridge vent, follow the manufacturers instructions. Typically, the ridge vent comes in 4′ sections that you nail to the roof using extra long roofing nails (>2″) that are nailed in at regular intervals marked on the ridge vent. The ridge vent is flexible and it is up to you to flex it over the peak and keep it centered. You will also need long roofing nails for putting the cap shingles over the ridge vent. To make the cap shingles you cut the tabs off of some extra shingles and use just the tabs. Start at one end and overlap the cap shingles by 50% or so, using two long nails in each covered corner that will go through the ridge vent and into the underlaying roof sheathing. Proceed down the vent until you get to the end. The last cap shingle can be put in place with roofing cement. I don’t have any pictures of the shingling process since by that time in the project I was in a pretty big hurry to get the heck off the roof.