First, although the top is "made from real mango wood" it is only a thin veneer. I started by building two frames (42" x 28") from 1.25" wide, 1/8" thick angle iron. I then used a MIG welder to run a bead of weld across the top and outside seams.
I flipped the second frame on it's face, lined up the legs, and welded the pieces together.
I now pretty much had a rectangular box with the angle iron open to the center. I've been looking on-line, through thrift shops and craigslist for large casters for a good price.
This system would work as rigid (non-swivel) casters for a number of different projects. To attach them, I drilled a 1/2" hole in the top of the caster bracket, as well as all four corners of the bottom rail of the frame.
I then ran a 3/4" long, 1/2" bolt through the bracket and bottom rail, and secured it with a nut.
I was really going for a "pallet-ish" look for the wood, but I've experienced pulling pallets apart (about as much fun as going to the dentist), and to try to find enough slats around the same size and thickness wouldn't be easy. The bottom shelf, I cut to fit inside the angle iron. Just make sure to notch out the corners of the OSB, underneath, so there is room to accommodate the caster bolts and nuts.
Secondly, I chose to add a carriage bolt in each corner to give a little detail to the top. To finish the metal frame, I selectively sanded areas with a fine grit flap disk.
I then played around with a couple different patinas that I bought while at Industrial Metal Supply. The frame, wheels, and wood all received 2 coats of wax to seal everything.
You hear of women creating beautiful things from wood, but rarely do you meet a woman that welds. I would suggest keeping someone close by to help you set your speed and voltage until you get some experience.