I won't copy and print someone else's work and put it on the internet, too much chance of getting in trouble for copyright infringement. I will tell you though, how I built a portable standup shooting bench. First I cut out a triagular piece of 3/4 inch plywood about 30 inches on a side. I nailed some short pieces of 2x4 pine with the ends cut off at a slight outward angle, say about 100 degrees, under the plywood, running from the corners inward to the center. I bevel cut the inside edges so that they would all kind of support each other where they came together in the middle. The corners of the triangular piece were cut off perpendicular to a line drawn from the middle of each corner out to the middle, leaving a two inch wide blunt corner. The 2x4's on the under side were made so the the angled ends set back from each corner of the plywood 1.5 inches.
Next , I figured out how high I wanted it to be. This is harder than you would think because it has to be just the right height to stand up at comfortably, but not low enough that you have to bend over any. I cut mine too long to start and had to cut some off all three legs till it was just right. The legs are made of 2x2's which actually measured 1.5x1.5 inches square, That's the reason the 2x4's underneith were set back from the corners. The 2x2's have to have both ends angle cut so when they are set up in their slightly splayed out position, the tops and bottom ends are paralell to the ground. The legs are then attached to the top by three long strap hinges that mount to the top surfice of the tiangle and run down the outsides of the legs.
About half way down each leg, I cut a small notch in from the outside edge. I purchased enough lightweight chain to run clear around the legs at the notched position plus enough extra to go across the triangle. The hinges on mine were left intact and can be folded over the top to collapse it flatways to be put in my pickup. The hingepins can also be removed if you want to and replace them with 16 penny nails. That way the hinges themselves could be broken down.
When you set this up, you have to fold over all three legs to the underneith position, then wrap the light chain around the legs at the notches, open one link at each end to form a hook. When setting this up, make sure that the end hooks to the chain in the middle of one side, then take the remaining tag end, go across and hook it into one of the other side chains out towards another of the corners. This pulls the legs in tight and the cross chain braces and maintains the tension. For as flimsy and lightweight as it is, it is amazingly stable when set up properly.
Mine is broken down and stored right now or I would have included a picture of it set up. I think I have given you enough information to build one if you read this closely. If you have any questions, ask away. Bob H.