Screen printing diy exposure units?

[sporadicity.livejournal.com]

Hi, I'm just starting to get into screen printing/silk screening and I was wondering if any of you have built your own exposure unit (light table)? I've been looking online and the only instructions I've found for building one is this one.

Can anyone point me to other places on how to make an exposure unit or clear instructions on how to make one?

Thanks!