Step 7:
(Picture 1)

Take two of the 2x4's that you cut into 72" lengths and place them side by side facing each other. You may want to elevate these onto something as we will be drilling and we need all the room we can get for the drill to go all the way in.

If you don't have one of those work horse things you can just elevate it with a second set of 2x4's as seen in the picture.

Step 8:
(Picture 2)

Take your two 32" pieces and mate them to fit with the two 72" pieces. Put them together so their 45 degree ends meet together and form a 90 degree angle.

Step 9:
(picture 3)

Place weight on both pieces of lumber where they meet. We are going to drill multiple holes through them to make it easier to start our wood screws.

Use a drill bit that is about the same size as the tip of your screw that you're using. This makes it easy to drill the pieces together but still gives the screw enough material to bite onto.

Step 10:
(Picture 4)

Screw your 2.5" screws all the way into the wood. Do not be afraid to continue screwing inward after the screw is flush with the wood. Most untreated 2x4's are soft wood and this works to our advantage. I used 3 or more screws per joint made. I used my own judgement when determining how many screws to make.

It's important to note that most of this wood is a bit warped as it is untreated (which is what you want. You don't want to buy treated wood). This is not a big deal as we bind the pieces together things will become flat/flush.

Repeat steps 7 through 10 until you have made 4 panels that look like Picture #5