If I hadnt already picked up an etch-o-matic etcher I would have built one of the home brew ones for sure. might still in fact. I find the etch-o-matic's hand unit is kinda bulky and can be difficult to get it where it needs to be.
Here's a site that also has a schematic diagram at the end. One of these days I build one, but right now I just use an old power supply and some alligator clips.