This is what I've been working on since Friday. I had started out thinking I'd just make a "mobile weed-killer", meaning some black plastic mounted on a wooden frame that I could set over the worst areas of the yard to kill everything off and start over. Then I got the frame made, and remembered that last year I'd considered making a primitive deck out of the old fence planks in the garage and figured, "Why not?" Well, there did turn out to be an answer to that: "Because it's no longer particularly mobile." However, I still have a few planks left, and I may put together another, more lightweight frame, that can be moved.
The planks have been in the garage since I bought the house. My best guess is that they were part of a fence blocking off the alley at one time. I have a suspicion as to why that fence was taken down, too. The ad for this house said "off-street RV parking." With a fence blocking the alley, there really isn't any such parking. So I'm thinking the realtor advised the former owners to take the fence down so they could put that in the ad. Can't say for sure, though.
Whyever the wood was there, this is the single largest thing I've ever built. It wasn't particularly complicated, as I just used the planks as they were without trying to cut them down at all. It was just "line up, drill, attach with screws." From this I conclude that the hard part of making a "real" deck would be the planning and cutting and leveling. The actual attaching part, while tedious and time-consuming, was very straight-forward. Particularly since I had a philips screwdriver attachment that fit my drill.