I've just finished the build of a small folding copter to travel with, which holds a gopro on a 3 axis gimbal, or a Canon S110 on a 2 axis gimbal. It's wider than it is long, and is about 460mm diagonally.
it weighs 1.7kg fully loaded with 5k mah 4s battery, FPV gear, gopro gimbal, and is running sunnysky x3108s 720kv motors with APC 10x4.5 props. Flight time is about 15 minutes. I've made the central plates both from 2mm FG plate, but this is unnecessarily heavy, so I will change the top plate for one made from 1mm CF.
I started with Angel's monoblock design, but then scaled the arm blocks down to fit 12mm arms. I modified the ESC32 brackets so that they could be stacked, and I also made some holes in them to stop heat buildup. I created brackets underneath these to hold both the receiver and the VTx. The legs weigh 8g each and just clip on tightly, so can be quickly removed for folding. They can also be zip tied on for a more permanent fit.
So far it's pretty much everything I've always wanted from a small copter. Super stable video with high precision control (thanks Autoquad), long enough flight times, clean video feed, and packs down into quite a small package for transport after removing four m3 bolts on the arms. The front and rear arms both fold back to all be together.
I'm not much of a designer, so it could be made to be prettier, but I'm happy with how it's turned out considering this is the first thing I've designed! Just need to figure out a way to run all the cables from the gimbal in a tidier way without restricting the movement.