Our new house has a screened in porch area that is great for sitting outdoors but getting away from bugs. This necessitated new furniture to make the space even more enjoyable. We were debating also making the cushions, but we found these blue ones for 50% off at a store called At Home. Overall, the cushions were about $150, the wood was about $300 and the screws were about $50. Considering retail couches sometimes go for over $1,000, I think we ended up ahead.
Read more to see how I built it
We drew up some basic plans. You’re welcome to use these plans if you want for personal use. Also note that the measurements shown here were adjusted slightly as I went along.
In a nutshell, there are two parts to the couch. Both parts are angled back at 105 degrees for the backrest. The structural supports for the platform are spaced at about 16 inches apart. I used pocket hole screws to conceal the screws. You can find a picture of that below.
Then we figured out how we wanted the back supports to work. That was a little tricky. We did some research to find the ideal angle, but then we resorted to just putting a piece of wood at different angles and deciding what was the most comfortable.
The first deck is starting to take shape:
For extra stability, I splurged for 6 inch wide Douglas Fir. They have some serious heft to them. This is the inside corner of the longer of the two couches. The legs here went on the inside so the other piece could sit flush against this piece.
With the exception of the pocket hole screws, I used 2.5” deck screws to attach everything else.
At this point, I got distracted and started thinking about how the end product would look. We tried our hand at making homemade wood stain. This was more or less a bust because we didn't like how it turned out. We mixed vinegar with steelwool, and vinegar with steelwool + apple cider. It brought out so much of the wood's tannens that it looked too gray for our taste.
This is the shorter of the two couches. I technically built it second, but it’s the best picture I have of how I attached the back supports. I used the same wood for the arm rests & back supports. The vertical pieces will be supports for the arm rests. 
This is the back of the longer couch. Lots of support.
How it looks from the front:
Here you can see the back slats starting to go on here (closest to the camera). This was definitely the hardest part of the project the slats angled back at 105 degrees. With a 45 degree miter beveled at 15 degrees. It’s simple now, but figuring it out & cutting it correctly was hard at first:
You may notice the top slat doesn’t have two screws on top of one another this is because it extends beyond the top of the back support. It still has plenty of support:
Look at how pretty those slats come together! I am very pleased with how it looks. I thought there wouldn’t be enough back support when sitting in the corner, but the thick cushions make it very comfortable. 
And from above, because I’m very proud of the symmetry:
Here are the two couches sitting next to one another in their intended L-configuration. I’m pleased with how the deck (where you sit) lined up so perfectly (it should; I spent nearly 20 minutes agonizing over measuring & remeasuring before screwing the second set of legs in). The natural wood tones here made us question if we really wanted to stain the wood or not.
Here’s another angle, with the arm rest attached. We took a cereal bowl and traced a radius to make the curved part on the arm rest. Then we cut off the wood outside the radius and used a belt sander to make it gradual all around. It gives it a great craftsman look.
Two arm rests! The arms & legs are made of Douglas Fir, which has a very appealing grain for me.
With cushions:
We picked out a stain called Gun Stock by Verathane. We also got wood conditioner to reduce blotchiness.
The stain was applied about 40 minutes after the wood conditioner on this one:
The stain was applied to the second couch one week after the conditioner, which lead to a much darker result. We also speculate that the can of stain might not have been fully mixed at first.
Here’s both side by side. They still look amazing. And this is before applying any polyurethane.
And finally with polyurethane:
