AKA "saw buck" -- I made one from scrap 2x4 lumber when we were building our house. I don't have any pictures, but basically, make two identical assemblies like this:
Then cross these two assemblies into an X and nail or bolt about halfway up. After that, I nailed some additional bracing across the bottoms to keep the X open, but left the tops open to allow access. Also added some horizontal bracing just below the crossed part. Basically, stiffen as needed for your anticipated use. Mine is beefy enough that I can dump 4' logs in from my front bucket. Sometimes I will dump in 2-3 at a time if they are skinny (more care required when cutting).
Standard lumber OK for verticals, but I used pressure treated for bottom. The spacing of the verticals should be set to whatever makes sense for your typical log length, knowing you will cut on the side of the verticals -- or space then wider if you have a short bar on your chainsaw and need to get in closer. You may want to add more verticals that would support your cut rounds, depending on how you like to cut.
Offhand, I think my vertical pieces were 4-5' long to give the desired height when crossed, so that I don't have to stoop over when cutting. I'd estimate that the crossed point is about 30" high. I made the sawbuck about 4' wide and spaced for 16" cuts.
I do remember seeing some plans on the internet, but they were somewhat limited to that person's vision/workflow (for instance, what works for a short person would give me a backache). So start with the basic idea in my sketch and dimension it accordingly.
