Here's a cart that has worked well for us. Designed to allow loading by wide-spread forks (on front-end loader in yard), and unloading by sling and overhead hoist (in shop).
I saw this cart at a flea market yesterday. This is the same conceptual design as the guilds "Timbercart". I guess the point is, you can build a similar design that could be lower to the ground? Maybe easier to load? This one could be made to work, though you'd have to pay attention to the height so that you are not stooped over when pushing it, or you'll end up with a sore back.
A great place to get wheels and an axle is from a fish processing plant, if you're near the ocean. I got a set with a solid galvie axle and 24" cast steel spokes with solid hard rubber for fifty bucks...it used to have a steel cart that carried fish, but the cart rusted out.
It's on the heavy side, but not much it couldn't handle.
I use a couple carts from the sardine industry from back a while. Steel wheels, 3/4" axle, hard wood frame and deck, sits about 14" off the ground. Works only on smooth floors. Nothing too big for it. It is not ideal but serves well.
The counterweight has only about 2" clearance. He assumed it needed to sit level.. Hasn't proved to big a problem as of yet, but if need be, I can have him hack it off and raise to increase clearance. The weight is just a tube full of metal waste from his shop.