There's a sticky about it or maybe it's in the articles area. Yes it's chocolate panels and squares are much easier than rounds.
You get mylar (plastic that comes on rolls) in the art section of your local craft store --and pour melted chocolate onto the plastic mylar and apply it onto the cake. There's some finesse here that you'll wanna practice--chocolate is all about temperature.
The shinier your plastic the shinier the chocolate.
well, that would be pouring chocolate out to make sheets and trimming to sizes needed while still semi-set.
then placing them one by one onto the cake -- a soft BC that hasn't crusted would be the "glue"
hint- tilt them up into place, using a stiff piece of cardboard to support them as you do.
this video, while talking about small items and using patterned transfer sheets, gives the basic principle of how to achieve a large piece of chocolate.
http://www.countrykitchensa.com/videos/chocolate_transfer_sheets_cutouts.aspx
in your case -- clear acetate (no pattern) and you'd be cutting out pieces the size of the each side of each cake tier.
the two threads K8Memphis- alluded to:
http://www.cakecentral.com/cake-decorating-ftopict-396793.html (click on link in first post -- it goes to same site I referenced, but a different video)
http://www.cakecentral.com/cake-decorating-ftopict-56654.html
While both of these talk about round cakes, for a square cake, it's just cut out the panels the correct size (remember measure TWICE, cut once) and then let them fully harden before placing on the cake (sort of like dry walling the cake in chocolate!)
If you don't want to have to worry about tempering your chocolate, use white candy wafers (like the Wilton)...I've done this and it is much easier to work with IMHO...great effect though....kinda sleek looking..better than some of my sloppy cakes lately...
I just found what I'm looking for...I'm in Canada so I always have trouble ordering anything without incurring duty charges...
Here's where I ordered them from:
http://www.chocolat-chocolat.com/c227935.2.html
well, that would be pouring chocolate out to make sheets and trimming to sizes needed while still semi-set.
then placing them one by one onto the cake -- a soft BC that hasn't crusted would be the "glue"
hint- tilt them up into place, using a stiff piece of cardboard to support them as you do.
this video, while talking about small items and using patterned transfer sheets, gives the basic principle of how to achieve a large piece of chocolate.
http://www.countrykitchensa.com/videos/chocolate_transfer_sheets_cutouts.aspx
in your case -- clear acetate (no pattern) and you'd be cutting out pieces the size of the each side of each cake tier.
Thank you Doug for that reference. I went to their site and watched the cake videos for fun and learned some new techniques! I NEVER would have thought of filling a sheet cake the way they did but OMG it's much easier than the way I do it!! 
BTW, C.K. is my FAVORITE cake supply store! Whenever we go to Ft. Wayne we stop! My kids groan when they see the parking lot because they know it'll be a few hours (unless they drag me out sooner). They just get upset because it makes our trip back to MI that much longer! 
You blessed my day, thank you! 
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