there are plenty to be found in art supply stores but they can be expensive and every one i've ever seen has required you to be plugged into an electrical outlet for power. sometimes having to deal with a cord while you're trying to turn the table to a different angle is just annoying so lets get on with this instructable so i can get back to the drawing board.
Step 1: Materials.
an acrylic sheet. you generally don't want a clear sheet because a translucent white sheet will help diffuse the light so it's a bit more even across the board. it should also be thick enough to write/draw on top of .177" thick should be good for most but if you're making a big light table you may want to get something a bit thicker.
walls and a floor. doesn't matter too much what these are made of so long as it's sturdy enough to hold up the acrylic sheet and take whatever pressure you put on it while drawing. needs to be opaque (doesn't let light through) and something white or that you can coat white on the inside somehow. just use your common sense and don't make it out of anything harmful to your health.
LEDs. personally i'd go with white but if you want a trippy hippy light table that's your call to make... you could probably hang that on your wall or something... yea.
Resistors. don't wanna burn up your LEDs.
Electrical Wire. spreading out your LEDs will help even out the light across the drawing surface.
Batteries. needs power
Battery holder(s). because holding them yourself gets tiresome.
Power switch. it's easier than taking the batteries out.