KBs are a fun way to mix up your workout. I've found em to be really good for high rep cardio work and building grip strength(see my avatar). But the damn things just cost too much- a 36 pounder ends up costing something like $120. I guess if you're really into them this isn't a lot, and they'll last forever. But I just use KBs from time to time for fun- I'd rather spend my $$$ on steel to bend.
Here's how to build your own.
1-1"x6" steel nipple (handle, external diameter is 1 and 1/4")
1-3/4"x6" steel nipple (through plates, external diameter is 1")
2-1" 90 degree elbows
2-1" to 3/4" reducing elbows
4-1"xshort nipple (don't remember exactly what they call the length on these, it's not a numbered length, but it is the shortest nipple I could find)
6-5 pound standard barbell plates (make sure the 3/4" pipe goes through all of these, the hole in some of my 5 pound plates are too small to use)
This configuration gives a 2 and 1/2" space between the handle and the top of the plates. Make sure everything is tight. I used a wrench to get things tight. And I check everything for tightness before every workout with it.
You might want to get all of the joints welded, or put some kind of lock tight on the joints. The plates are loose on mine and rattle, so I stuff a piece of foam rubber between them. Dragon Door kettlebells have a curved handle which keeps your hand in the same place. This handle is straight and my hand tends to slide to the side, and I have to re-adjust my grip. I plan on buying a DD kettlebell eventually (eventually I'd like to have a complete set or 2). This will do until I can afford it.
I'm not going to give detailed instructions on putting it together. You should be able to figure that out from the picture (the bottom picture), but put the top half together, including half of the 2 unions, put the bottom half together, including the other half of the unions, then attach the halves of the unions together.
I can't guarantee that this won't fly apart when you use it, all I know is that mine is solid. Don't use it around anyone or anything that you don't want to hit with it.