Find a sturdy flat piece of steel for the base. An old junk disc brake has all you need. It's heavy, flat, easy to clamp, already has holes drilled for mounting.
Step 2: The post
You need a post that will allow for clearance of the wheel you're truing. It must also be sturdy. You don't want it flexing or vibrating while you're spinning or moving the wheel. I used a piece of 1"Dia x 18" long steel pipe.
Step 3: Mounting the wheel
For a little extra flash, i removed a front wheel bracket from a junk bike to mount the wheel. You can use a nut or a washer welded onto the post, or just simply drill a hole through the post. Now tighten the nuts on the skewer until it is tight. Attach the magnetic base dial indicator so it rides on the rim of the wheel.