Step 4: The top trim
Now that the sides of the bed are assembled, time to put the top on. The width of the 4x4 plus the outside trim means we need about a 4.5" wide board. Thus, we had to buy the 1x6s and rip them to the appropriate size. So, you know, do that. This is what the table saw is for. I even took a picture of it (the saw was off at the time, don't worry).
Miter them corners up
Now comes the fun part. We are going to miter the corners of the top frame, so that it doesn't look like the bed was made entirely by a third grader. To do this, you need a miter saw. Turn the saw to a 45 degree angle. Cut the angle on both side pieces. Then you can measure the length they need to be and cut them off straight at the right measurement. Way easier than a precise measurement on a miter cut. For the foot you will obviously need to make two mitered cuts. Measure using the fat end. Make sure you also take into account the width of the saw blade, and where it lines up to your cut line. Good job. Now do a test fit to see that everything is playing nicely (There's even a photo of this to check your progress.)
Add mini studs
This step is probably completely unnecessary, but again, I am a man that enjoys overkill. So we're going to go along and place mini "studs" along the edge of the trim for further support for the top and side trim. To do this measure exactly the height from the frame stud to the top of the pine. Now take your 2x2 and cut about 15 or so pieces to the same height. To make this easier, clamp a scrap piece of wood on the end of the miter saw the appropriate distance from the blade, so you don't have to measure every piece, you can just butt it up against the scrap and they'll all be the same length. There is a picture here to show what I mean also.
Now arrange, glue and nail these along the perimeter of the bed (as shown). When that is finished, you may apply the top trim by gluing clamping and nailing in the appropriate locations.
Give it legs
As nice as the 4x4 legs look, you need to make them even with the trim. So what I did was cut some scrap 1x6 pieces to 1/4" less than the height of the leg. This allows for some room so that the 4x4 still supports the bed and not your arbitrarily placed scrap wood. And it's long enough that it looks like that's all its resting on. Anyway, glue and nail these pieces in. I only did the outside corners, and mitered the edge, to make it as clean as I could make it look.
Now it's finally starting to look like a bed!