Use 2x material for your purlins and 1 1/2" screws to attach the metal sheets. The purlins are another great time to use used material and you don't even have to pull the old nails. To speed the process, cut some blocks sized to fit between your rafters or trusses ( ~2' ) and just nail one of the blocks under any location that has a seem. That way you aren't wasting time trying to cut purlin boards so the seems are directly over a rafter board.
The most likely area for wind to start working on a metal roof is right at the bottom. To make it last, make two runs of purlin around the bottom of the roof, lowest one with treated lumber. If you don't cover all the purlins with Tyvek, at least put a thin strip of tar paper over the 1st 2 or 3 runs up from the bottom of the roof.
Set the flashing for septic vents such that it is overlapped by either the ridge vent or some other seem in the roof.
Unless you can rig a spooler up, as seen below, you will want to have a helper to wrap the house with a vapor barrier.
Windows and exterior doors are installed next, as well as any exterior trim. The lumber yard can often provide temporary construction doors that you can use until the house is ready to paint. The purpose is to keep your nice new exterior doors nice and new.
Now you are ready for whatever exterior siding you have chosen. If there is any chance of a wildfire in your area, use a thick, non-flammable exterior for your house. The rock crew I found had an uncle who owned the rock quarry. They were able to get the rock and do the work for less than I would have been able to get the rock for. As covered in the video below, make sure you have openings for any A/C, water, dryer vents, or electric lines that you need to pass through your wall.
I liked the idea of vinyl siding because it would never need painting, but next time I would take a hammer with me when I shop for it. I'd ask for a sample and then I'd whack it with the hammer and see if it cracks. The stuff I got does not hold up well to hail. Fortunately I did save all the scraps, and so I had leftovers to make patch repairs later.
Wait to pour the driveway until you are sure that you can keep any heavy delivery trucks OFF! Plan ahead and set form tubes for deck piers, set forms for any porches, walks, or out buildings; and pour all of these at the same time as the driveway.
The last tasks on the outside are to finish out any decks or porches. The timing doesn't matter much on that though.