This is a replica of the Weighted Companion Cube from the game, Portal (1). It is Identical to the Storage Cube apart from it's symbol. but, this is different to Portal 2's Cubes.
I have looked at other fan made cubes, and I couldn't be sure if they were accurate (while free :3), so I made my own.
I give my guarantee I have tried to keep it very accurate. (I'm trying to build it after all)
how I made:
I took photos from game and merged them to get a parallel projection of the cube.
For size, I took comparisons to the turret in game and to Valves turret in real life, (from one of Valve's videos). and also measured using in game cans of beans! :3 (6 x 4' diameter cans)
I took the cube to be a round figure of 2 feet, because also all the other measurements meet some rational number (a fraction) of the likely used unit, inches. So I am confident this means its supposed to be 2 feet wide, but that is quite big... so its up to debate. I added some quick colors/ textures too, for fun :3
(this is my first model, so I hope it works for you. if not, it is also at 3dwarehouse)
The design of this Cube belongs to Valve.