I love the look of the mosaic cakes that I've seen here on CC and would love to try to make one. I was thinking I'd like to make my mosaic pieces out of chocolate, but wasn't sure if that would be the best route to go? Would another medium work better? If I use chocolate, would I just need to melt it, pour it into a thin sheet, then break apart? TIA!

I use GP. Rolled super thin, and cut at angles in a back and forth motion with a pizza cutter. Super sturdy, nice and even, and then I break pieces up from the pieces I already have.

That's how I'd do it. Be aware that breaking chocolate will result in very uneven pieces and might not finish the way you want. If you can cut the chocolate when it is *almost* set it would be better but don't know that that's possible. You'd have to work w/very small amounts and quickly.
For a more perfect end result use fondant rolled thin and cut.

Thank you both for the advice! I think I may try the fondant or gp approach this first time around.