So, for the shed project I'm working on, we've gotten to the point where we need some doors on this sucker. I tried making a couple by simply screwing some 2x4's together like they were studs, but we quickly discovered that without a diagonal brace it's not stable. So unstable, in fact, that simply sinking a second screw at a corner could pull it out of shape. The diagonal worked, but it was a major pain to make adjustments to the door: finding out you need to shave off 1/8" means having to basically take the door apart to do the cut. There's also the problem that it's kind of hard to find threshhold flashing that's 3 3/4" wide.
So, I decided to finally try out a lap join and just turning the 2x4's so their faces were to the front. It's a heck of a lot more work and takes longer, but holy cow was it worth it. I basically ended up with a much thinner door (1 1/2") that fits the flashing perfectly, is much lighter, doesn't need another brace, and is dead simple to get to 90 degrees in the corners.
The technique I used was pretty caveman-style. Basically just measured the boards to fit (no need to knock of 3/4" on the ends since we're going to lap them), cut, and then marked off 3 3/4" back on the board. I then set the circular saw to 3/4" depth and just made a bunch of cuts across each end of the board that needed a lap, knocked out the remaining wafers with a hammer, and planed down the lap to get it as close to 3/4" thick as I could.
The board on the left is what it looks like after planing, the right side is the before photo. I did just enough for the lap to kind of "feel" smooth, but as you can see it's still got the marks from the circular saw in there. I tried using a chisel to clean up the lap, but I found that just using the plane got the job done quicker and avoided the risk of gouging deeper into the wood.
After cleaning out the laps, the last step was simply to assemble the boards. What I did for that was to simply lay the stiles (sides) of the door down on their backs, and put the rails (top and bottom) across the laps. I started at one corner with a 1" screw in the center, used a speed square to make sure it was 90, and then sunk in a second screw in to lock the join in place.
In the end, it was a wash in terms of the time it took to make the frame. The lap join took a lot less time (and frustration) to assemble, but also took a lot more time to prepare the materials. And a lot of that time was spent with the ciruclar saw (ow, my ears). There's probably an easier, more efficient way to do the lap cuts, but for a first stab at it worked out pretty well.