Have you built a light box?

Nope, I've never made one before. I am going to a lighting presentation at my local photo club this week, so who knows! Maybe that will be one of the things we'll learn there!

If you're looking for online instructions, I usually check YouTube for how-to videos. I find watching a video to be more helpful than reading written step by step instructions!

No, I never have and I'm interested in building one. I need to create better lighting for my jewelry photos, especially in the winter when the I only have about an hour of prime natural light in my craft room (of course that time occurs while I'm at work )
That only leaves weekends for me to do my photos and with craft season in full swing, I won't have much time to get my photos done (and I know that it will be overcast or raining on the weekends I don't have a show)
If I can find a link to making a lightbox, I'll post it here. If you find a site, please share! Please???

What exactly is a light box and what's the purpose of it?

I can honestly say I've never built my own light box, mainly because I don't know what the heck you are talking about. What the heck is a light box, how is it used, and how do you build one? It sounds like it would be a pretty interesting thing to see, though.