OK, I actually built the skimmer for a hot tub but figure it's probably more applicable to above-ground pools so posted here instead.
Background -- I have a 6 foot diameter cedar hot tub, purchased with no pump/jet/filter because I wanted to be able to use it through the (very cold) winter without having to worry about the plumbing freezing up. Picked up a cheap Intex 1000 GPH filter/pump (AKA "the kidney") so I could get some filtration between uses, but initially had some trouble keeping the ends of the hoses in the water.
A couple of days ago I realized that if I could securely fasten the included fittings onto the ends of the hoses (I say securely because the hose clamps provided are *not* enough to stop the hoses from slipping off) I could hook them under the edges of the benches and keep them well positioned in the water. Ran the pump that way for a couple of days doing my first SLAM, and realized that the only thing I was missing now was a skimmer to get all the dead insects etc... off the surface.
Spent a bit of time looking at adapting a Hayward skimmer, and in the process stumbled across a few DIY skimmers on YouTube. They seemed a lot simpler than I expected, basically just something to let the water pour in from the top and accumulate enough at the bottom so the pump suction fitting always had a supply of water. I couldn't believe it was that simple so simulated it by holding a bucket on an angle underwater and holding the suction tube inlet at the bottom of the bucket... and it worked !!
I looked into building a DIY skimmer from 3" PVC and reducer fittings but kept coming back to the same problem -- the hoses on the Intex pump are not the same size as *anything* else with the possible exception of stainless steel tubing (haven't tried that yet), and so no matter what else I put together I would still have a problem connecting the hose. That led to the idea of cutting up one of the fittings and building that into the skimmer assembly... and from there it was a short jump to the final solution.
Built an open box out of cedar scraps -- 2x6 for front/back/bottom and 1x5 for the sides, with the sides lower than the front/back so water could get in. I made the inside dimensions of the box large enough that the suction hose *with* the fitting and strainer basket on the end could fit inside, but small enough that sliding another piece of 2x4 or 2x6 inside would trap the strainer basket at the bottom of the box, taking care of the connection problem.
And that was it. First picture shows how the fittings were hooked under the benches (I still clip the return hose under the bench like this) and the second picture shows the skimmer box with suction hose running down to the bottom. It's not pretty, but after running for ~30 minutes all of the bits and pieces floating on the surface of the water were gone. I think I might get better water circulation with only one side open (away from the return) so will try closing off the other side as a next step.
Hope this is useful to someone... or at least makes you feel good about having a real skimmer instead of some ugly DIY affair