Here is the plans I used for my lightbox. LINK & directions LINK.
Although, there are a few things you should note. This box holds 16 BLB (4x4), not the 8x4 that was stated (I need to change the design posted). You could fit more if they were placed closer together. In addition, you may have to modify the design some depending on the height of your contact or vacuum frame. Because I recently moved on to a vacuum frame I'll have to add some sort of extenders to raise the height of my lightbox.
Since I built the box I have decided to add the remaining lights, as I had only started with 6, but the company I was buying the bulbs from no longer keeps an inventory of the bulb, so I had to wait about 6 weeks to recieve them.