Need help selecting material...

I'm guessing there is an easy answer to my question, but I just don't know the answer. I want a set of wheels for my landscape rake like the picture below, but like a lot of other folks I don't want to pay $2-300 for the wheels. I can make these, I'm confident in that, but what I don't know is how to select the right piece of "pipe" that will allow the shaft on the wheel to fit. For example, if I got 3/4" round bar for the wheels what is the best way to select material for the bushings to adjust the height and the small piece attached to the square tubing? Do I just get 3/4" black pipe and maybe run a drill bit through the pieces after I cut them down? I have the same question honestly about finding square tubing that "nests" together like a trailer hitch/receiver combo. The metal supplier I doesn't show ID dimensions of anything and its not really setup for me to walk around to test fit pieces.

Any advice?